♪♪ ♪♪ ♪♪ ♪♪ -Today on "America's Test Kitchen," Lan makes Julia rainbow cake and Erica makes gluten-free, rainbow sprinkled cupcakes.

It's all coming up right here on "America's Test Kitchen."

"America's Test Kitchen" is brought to you by the following.

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♪♪ -For my daughter's ninth birthday, I had a ton of fun making a monstrous rainbow cake where every layer was a different color.

Although I did get in a little over my head because the finished cake weighed a whopping 36 pounds, and it took both me and my husband carrying it on this huge cutting board with the candles to get it to the table at birthday time.

So I'm hoping you can break down the layer cake so that it's a lot easier to make 'cause it's -- it really does bring the house down.

-Step one, we're not making a 36-pound cake.

-Check.

-Um, step two, to make this a little faster, how about you cook with me and we make the cakes together?

-Yeah, because we have to make six layers, right?

-It is a lot of layers.

If I were at home doing this -- and I actually did do this two weeks ago for my nephew's fifth birthday -- I had to make three cakes at a time.

And it -- you know, it's not difficult, but it takes a while and so this will speed it up.

So we're going to be making cakes that are reverse-creamed -- they've got a really fine, moist, fluffy, tender crumb -- and we're making white cakes because that will provide a nice, blank canvas for all the colors.

-Yes.

-So we're starting with a cup of whole milk.

-Mm-hmm.

-And to that we're going to add six large egg whites.

-Alright.

-Just dump them in.

I've got the milk in a 2-cup measuring cup.

It's just large enough to hold everything, and it'll make incorporating the wet ingredients a lot easier.

Next up is 1 teaspoon of vanilla extract for a nice flavor, and you should have a little mini whisk over there.

-[ Chuckles ] -So cute right?

And, you know, nothing complicated here.

We just want to blend those whites and that milk together.

Alright, this looks pretty good.

Again, it doesn't have to be perfectly combined, which is nice.

-Okay.

-Next up, our dry ingredients.

-Mm-hmm.

We each have stand mixers here, and I have cake flour in each bowl.

It is 2 1/4 cups per batch of cakes, and we're using cake flour because it's a low-protein flour that'll keep the cake tender.

-Mm-hmm.

-To that we're going to add sugar.

Now, this is a high-ratio cake.

It's got a good amount of sugar in it.

And sugar's hygroscopic.

It holds on to moisture, and it keeps that cake moist.

-Alright.

And right to the flour?

-Yep, add it right to the flour.

This is 1 3/4 cup of sugar apiece.

Next up, the leavener.

We're using 4 teaspoons of baking powder.

-Wow, that's a lot.

But then again, we're each making three layers.

-We're making a lot of cake here.

And lastly, for some seasoning, 1 teaspoon of table salt.

Now we'll just fit a paddle onto here and give it a mix.

We're going to mix on low speed because these bowls are quite full.

And just until everything is well combined.

-Okay.

-Mine looks great.

How about yours?

-I'm good.

-I have 12 tablespoons of butter for you, 12 tablespoons of butter for me.

Now, this is unsalted butter.

It is at room temperature.

-Yeah.

-In fact, everything we see here is at room temperature.

I don't want the cold milk causing the butter to seize when we combine things.

-Makes sense.

-So we're going to pop the butter into the mixer one piece at a time.

It's okay to take your time at this after you get all of them in, you want to let that mixer run until we have just pea-sized chunks of butter.

Usually takes about a minute.

-Okay, so these are all pea-sized pieces.

-Okay, so next up, we're going to turn these back on low.

We're going to drizzle in just half of this liquid mixture.

-Okay.

-And then once you get that liquid in, notice most of that flour is not dry.

-Mm-hmm.

-We'll crank this up to medium-high and let it go for about a minute.

-Okay.

[ Mixer whirs ] -Mine looks pretty good.

-Great.

Let's turn these back down to medium-low.

-Alright.

-And now we'll get the rest of this liquid in.

-Oh, as I add the liquid, the batter really does loosen up.

-Yeah, and you really want to be working at medium-low here.

Otherwise little bits of milk or egg might get flung out of the mixer.

It's been about 30 seconds, so let's have a look.

So let's get these bowls off the mixers.

We'll give this a quick mix by hand to make sure that any bits stuck to the bottom of the bowl get incorporated.

-Okeydoke.

Oh, I see what you mean by doing the last bit by hand.

There are some pockets of thicker batter down in there.

-Yeah, yeah, we just want to mix those in.

Don't want any dense spots in these cakes.

Now that these are mixed, let's ditch these stand mixers, get some cake pans out, and start playing with some food coloring.

-Ooh, I like it.

-Julia, I have six bowls for our six cakes here, and what I'd like you to do is to divide your batter evenly amongst the bowls.

I like to make sure that I'm using bowls that are the same size, 'cause then I can eyeball it.

-Yes.

-No measuring required.

Just make sure the batter comes up to the same level in each bowl.

This looks great.

-Yeah.

-Nice work.

-Looks very organized.

-You know, this is a little atypical for me.

So I have our food colorings out here for us, and these are gel-based food colorings.

They are just more intense, more vibrant.

Which means we don't need to add as much.

We're not going to, like, thin down the batter, emptying two containers of those, like, water-based dyes into our batter.

-Gotcha.

Okay.

-You're going to need 1/2 teaspoon of the red food coloring.

-Okay.

-Now, for the orange and yellow, those are a little bit more intense.

You'll only need 1/4 teaspoon.

-Okay.

-While you're doing that, I'm going to get our green, blue, and purple down.

-Mm-hmm.

-It's going to be 1/2 teaspoon of each of these colors.

-Okay.

Oh-ho-ho-ho.

That's a good red.

-Now, these amounts are recommended, and if you're using a different brand, you might need a little more or a little less... -Mm-hmm.

-...so, you know, don't be afraid to add a little more if you feel like you need it.

-That looks perfect.

-Right?

Let's do a little bit of cleaning up, and then we'll get these batters into cake pans.

-Okay.

-So, I've prepared these cake pans for us and, a lot of recipes, you'll see them say, "Grease and flour the pan," and that's good, but we've actually added a parchment circle to these pans, as well.

Gives us a little bit of insurance that that cake comes out in one piece.

Let's transfer these batters to the cake pan.

You'll just dump them in, smooth them out, and then we'll move on from there.

-Okay.

Now, do you wrap the pan on the counter?

-I do.

I want to make sure that any of those big bubbles get forced out of there.

-Mm-hmm.

Now we just need to get these in the oven.

I've got two ovens going at 350 degrees.

I have the oven racks on the upper-middle and lower-middle position.

You're going to pop two on that upper rack, one on the lower rack.

Let them go for about 20 minutes, and halfway through, we'll go in and spin those cake pans and flip them so that you got one on top and two at the bottom.

This helps them bake evenly.

-Ha-ha!

I love that the colors stayed.

They didn't diminish at all in vibrancy.

-Not at all.

They look great.

Thank you.

-I'll get this one.

-Mm-hmm.

Set this one over here.

And let's go get the other three.

-Okeydoke.

Oh-ho-ho-ho.

-This looks great.

-Yeah.

-Let's make sure these are done.

Just a quick toothpick test.

Nice and clean.

-Perfect.

-We'll let these cool a little bit just so that the pans are easier to handle.

It takes about 10 minutes, and then we'll get them out of the pan and let them cool all the way.

That takes two hours.

Julia, while those cakes are cooling, we're going to make an American buttercream to cover that cake.

-Mm.

-It is the easiest of the frostings, and it tastes amazing.

It starts with a pound of butter.

To that, I'm adding 1 tablespoon of vanilla extract, 1/4 teaspoon of table salt, and then, last up -- and this is a little bit of a departure from a traditional American buttercream -- I've got 1/4 cup of heavy cream.

You'd often see milk in these recipes.

-Mm-hmm.

-We like to use heavy cream because it adds a little bit of silkiness to the buttercream.

It's just -- It's lovely.

I'm just going to mix this together with a paddle.

It'll run for about a minute, and I'm just looking for everything to come together.

I want to get this up to medium-high, but I'm going to go slow so we don't get sprayed with cream.

-[ Chuckles ] [ Mixer whirs ] Awesome.

It's been about a minute.

You can see that there aren't any chunks of butter in there, and that's really all I'm looking for.

I will now add the sugar to this.

This is 4 cups of confectioners' sugar, and confectioners' sugar is great for this 'cause it's really fine, it dissolves almost immediately, there's no grittiness, but I find it tricky to, like, spoon the sugar into the bowl, and I like to kind of just put it on parchment and just, like, make a little sugar slide.

-[ Chuckles ] That's a big sugar slide.

-Right?

So we'll let this mixer run on medium-low.

I don't want to spray sugar everywhere.

-Mm-hmm.

-And I'll take my time getting that sugar in so that I don't make a mess.

After it goes in, we'll let this run for about four minutes just to really combine that sugar.

[ Mixer whirs ] So it's been four minutes.

You can see it's already looking smoother and a little bit lighter in color.

What I'm going to do now is crank this motor up to medium-high, to really work some air into there.

It'll really lighten it up, and when we come back, it'll be even paler in color and more voluminous.

[ Mixer whirs ] So this will be ready in five minutes.

[ Whirring stops ] Check this out.

-That's beautiful.

-Isn't it?

-Yes.

-This is just 5 cups of buttercream, and we need 10 all day to frost this cake.

So I'm going to scrape this out into a bowl, let it hang out while I make another batch.

-Okay.

-Julia, let's decorate this cake.

I can't wait.

This is the best part.

-Alright.

This is fun.

-So, first up, I'm using a cake stand here.

I think it just makes everything easier.

You could just certainly build this just on a platter.

And if you were doing it on a platter, I would line the edges of that platter with parchment strips just to keep the cake from slipping.

I'm going to put a little dab of frosting in the center of my stand, and that's to anchor that first layer so it doesn't move around as I'm working with it.

In between each layer, I'm putting 3/4 cup of frosting right in the center, and there's not really a trick to this.

The right tool is really important here.

It's worth it to use an offset spatula... -Mm-hmm.

-...but I'm really just spreading this frosting all the way to the edge of the cake.

And I'm not worried about bits of frosting sneaking past the edge by a little bit, 'cause we're going to put more frosting on the side.

And I know it looks like there isn't a ton of frosting here, but... -When you add all the layers together, it's going to add up.

-Yeah.

So we'll just keep working our way up.

The other thing I want to do as I build this is to make sure that I am centering the layers.

-It looks good.

-Yeah.

-Alright.

-It's nice.

Last layer.

-One last layer.

That is a beautifully, evenly frosted cake, Lan.

-Thank you.

So 3/4 cup for the top.

-Mm-hmm.

-And then I'm going to use half of the remainder of the buttercream to crumb-coat this cake.

What that means is I'm just going to kind of not slap a layer of buttercream on, but I'm not going to be super meticulous about making sure that the frosting is perfectly smooth.

The purpose of a crumb coat is to glue any crumbs on the cake to the cake itself... -Mm-hmm.

-...so that when you come back and add the final layer of frosting, it just gives you a more professional look.

I'm just going to continue working on this, and, once I'm done, it'll go in the fridge for 15 minutes to firm up.

-Alright.

-Julia, I had this cake in the fridge for 15 minutes just to set up that frosting, and now we can finish it.

-Okay.

-I like to start at the top, and I'm not measuring this time because I have all this frosting to work with, and so it's just a matter of getting it on and making it look good.

-Alright.

-I'm pretty generous with the amount of frosting I'm applying.

I'm just working my way around the cake.

Taking my time with it.

So I'm almost done here.

I've just got one last little bit to go.

And we'll just hold it vertical, resting on the bottom of the turntable.

Give it a spin.

Okay, so here's my little trick for kind of a lazy way to decorate this cake without making it perfect.

-I'm in.

-I'm just going to take my little offset spatula, press it gently against the cake, and I'm going to spin this table to kind of put a shallow divot.

And as I make my way around, I'm going to bring this up... -Mm.

I like it.

-...to create a little ribbon effect... -Yep.

-...and every so often you got to go and get rid of the extra frosting that the spat picks up.

You can make this super neat.

You can make it a little bit more irregular.

It's really up to you.

That's it.

-It's gorgeous.

-So simple, right?

-Yep.

-You ready?

-I am ready.

Alright, the big reveal.

-Alright, here we go.

-Ah, look at those colors.

-They're beautiful.

-They're beautiful.

Mmm.

-It's a good cake, right?

-Mmm.

-Usually, when you see a cake this pretty or this decorated, you think, "Ah, that looks cool but it's not going to taste that good."

This actually tastes terrific.

-It's moist, it's fluffy, it's light.

It tastes great.

-Mm-hmm.

This tastes way better than the cake I made, I have to say, and was much more manageable.

Lan, this is amazing.

Thank you for showing me how to do this the right way.

-Any time.

-So if you're ready to put a whole bunch of color into your cake, use egg whites and a reverse-creaming method when making the cake layers, use gel food coloring to get vibrant colors, and cover the cake with a crumb coat before adding the frosting.

From "America's Test Kitchen," a showstopper of a recipe for rainbow cake.

That purple layer is so fluffy.

-Right?

-It's so impressive.

-I'm going through a lot of cake.

-[ Chuckles ] ♪♪ -Being gluten-free doesn't mean you can't also taste the rainbow, so Erica's here today to show us some whimsical little cupcakes with all the colors.

-Yeah, gluten-free does not mean that you have to sacrifice flavor or even texture.

-Mm-hmm.

-And, too often, gluten-free baked goods bake up tough or dense... -Mm-hmm.

-...but these cupcakes are going to bake up light and fluffy, and it all starts with making our own gluten-free flour blend.

-It does, doesn't it?

-Yes.

-I have 24 ounces of white rice flour... -Mm-hmm.

-...and to that I will add 7 1/2 ounces of brown rice flour.

That's going to add some nice flavor.

-Mm-hmm.

-And I have 7 ounces of potato starch... -Mm-hmm.

-...and 3 ounces of tapioca starch.

Starches serve as nice binders.

-Mm-hmm.

-And 3/4 ounce of nonfat milk powder, which is going to help with browning and also add some flavor.

So I'll just whisk that all together.

So we are going to transfer it to our airtight container because it is more than enough for one batch of cupcakes.

But what's great is that you can pop it in the fridge -- it'll last for up to three months -- or in the freezer for up to six months.

And when you're ready to use it, just be sure to bring it up to room temperature.

So we have our gluten-free flour blend, so let's start preparing our cupcakes.

-Alright.

-So to get started, we want to start with 6 1/2 ounces of gluten-free flour, and it's always a good idea to weigh the ingredients anytime you're baking 'cause that ensures that you get accurate, consistent results every single time.

So we have our flour, gluten-free flour weighed out, and to the flour we're going to add in a teaspoon of baking powder, 1/8 teaspoon of baking soda, and 1/2 teaspoon of xanthan gum.

-Aha.

Good, old xanthan gum.

-Yes.

So the dual leaveners are going to ensure that we get a nice rise, and the xanthan gum is going to provide some much-needed structure that's lacking anytime you bake without gluten.

And I'll finally add 1/2 teaspoon of salt.

So I'll just whisk everything together and our dry ingredients are all set.

So let's get started on our wet ingredients.

-Okay.

-I have 4 ounces of chopped white chocolate... -Mm.

-...and to that I'm going to add 6 tablespoons of vegetable oil.

What's great about these is it's really going to add a boost of flavor.

And the combination of the chocolate and the oil is really going to give us that plush, tender texture that we want.

-Mm.

-So I'm just going to take this in the microwave and microwave it on 50% power for two minutes, stirring it occasionally until the chocolate is completely melted.

As you can see, our white chocolate is completely melted -Mm.

-...and we are just going to let this cool while we mix together the rest of our wet ingredients.

-Okay.

-I have 2 large eggs and to them I'm going to add 2 teaspoons of vanilla extract and whisk them right together.

What I love about this recipe is that there's no extensive whipping or creaming.

-There's no electric gadgets out here at all.

-Not a gadget.

And that's great because it's really simple.

And because there's no gluten, there's no fear of overmixing.

-Alright.

-Yes.

And then we'll add in 3 1/2 ounces of sugar, and we'll add in our white chocolate mixture and 1/3 cup of sour cream.

-Interesting.

-Yes.

The sour cream and the white chocolate and oil are really going to add that plush richness that we really want and love.

And now I'll just whisk it all together.

And it really starts to thicken up even as you whisk it together.

Beautiful.

Our wet ingredients are ready, so we can go ahead and add in our dry ingredients.

And now I'll just whisk it all together.

-Comes together so easily.

-It really does.

Beautiful.

That looks great.

-Mm-hmm.

-Now, to really make it a true party, you know what we have to add, right?

-Yeah, some color.

-Oh, yeah.

So 1/4 cup of rainbow sprinkles really is going to make it so festive.

Our cupcake batter is ready... -Alright.

-...so we're ready to get scooping.

-I see you have rainbow liners.

-And for perfect portioning every single time, I love using an ice-cream scoop.

It really ensures that we get equal amounts of cupcake batter amongst each cupcake.

This is just over 3 tablespoons, so we'll just use a scant scoop or just evenly divide the batter.

-Nicely done.

-Thank you so much.

Our cupcakes are perfectly portioned, so now we can head over to our oven.

They're going to bake at 325 degrees on the middle rack for 20 to 22 minutes, and we're going to rotate halfway in between to ensure we get even baking.

-Ooh, those smell good.

-Yeah they do.

Mm, these look lovely.

Perfectly golden brown.

They look so good, but just to make sure that they're done.

I like to do a toothpick test.

-Okay.

-So I'm just going to take a toothpick, and I'm going to stick it right in the middle of one of our cupcakes.

And if it comes out clean, then we know the cupcake is ready.

-Perfect.

-So these need to cool for about 10 minutes in the tin, and then we'll remove them from the tin and place them on the cooling rack to cool for another hour.

-Alright.

-Our cupcakes have cooled completely.

I have 2 cups of vanilla frosting, and to that I'm going to add 2 tablespoon of rainbow sprinkles.

-For color!

-Oh, yes.

We've got sprinkles in our cupcakes and in the frosting.

Never have too many sprinkles.

-No.

There's no such thing.

-There is really no such thing.

And I'm just going to mix them right in.

Beautiful.

That looks so good.

So now I'm just going to fill a couple of piping bags.

I'm just going to fill them right up.

-I'm so glad you gave me my own frosting bag 'cause this is half the fun.

-It really is.

-Oh, and it's fit with a star tip.

-Oh, yes.

So the star tip is going to give it a -- such a cute design.

And I like to leave, like, a little room around the edge of the cupcake, and it just makes it so much fun 'cause you can see the sprinkles in the cupcake, but you can also see the sprinkles in the frosting, too.

-Alright, I'm going to let you do one to show me how it's done.

-Alright.

Just like to spin this guy around... -Yep.

-...press my frosting all the way down.

-Mm-hmm.

-And then I just take it and start just a little bit from the edge, work a circle around, and a bit up.

-Nice.

Oh, I see what you mean by leaving a little bit of an edge.

-Yeah.

-Alright.

Those are really sweet-looking.

-These cupcakes look absolutely beautiful, Julia.

-Mm-hmm.

-But you know what would make them even more fun?

-More sprinkles?

-You've got it.

[ Both chuckle ] So shall we?

-Yes.

Just -- -Alright.

-As many as I like?

-As many as you like.

-Whoo-hoo.

-There is no wrong way to do this.

-There really isn't.

-It's just really about customizing it to what you like.

It makes it so much fun.

-Aww.

Those are the sweetest little cupcakes, Erica.

-I love them, too.

So what do you say?

It's time for the best parts.

-Yep.

The eating.

[ Chuckles ] -Oh, yeah.

So -- -Which cupcake you going for?

-Mm.

-Yep.

-I am going to take this one right here.

-Nice.

Nice, tall frosting.

-Mm-hmm.

-Alright.

What it really comes to cupcakes is about the taste.

-It is.

-Going all in.

-Alright, I am, too.

-Ready?

-Yeah.

-Cheers.

-Cheers.

-Mmm.

[ Chuckles ] -Mmm.

-I love the texture of the sprinkles, but the cake -- -Mm-hmm.

-I'm just going to pull out a little bit of cake and just eat it separately.

-Mm.

-Mmm.

If I hadn't watched you make it and known -- or been told that it was gluten-free, I'd have no idea.

-Yeah.

-It just tastes like a delicious, somewhat chocolaty, rich birthday cupcake.

-Oh, yeah.

I love that you can still taste that richness from the white chocolate.

-Mm-hmm.

-It's so subtle, but it's there, and that sour cream just brings it all together.

-Erica, these cupcakes are fabulous.

Thank you.

-My pleasure.

Thank you, Julia.

-So if you want to sprinkle a little fun onto your cupcakes, start by adding baking powder, baking soda, and a little xanthan gum to the batter, stir in some melted white chocolate and a little oil, and don't forget the frosting with lots of extra sprinkles.

From "America's Test Kitchen," an easy and very whimsical recipe for gluten-free rainbow-sprinkle cupcakes.

You can get this recipe and all the recipes from this season, along with our product reviews and select episodes at our website, AmericasTestKitchen.com/TV.

You ever taken the bottom of the cupcake and put it on top and made a cupcake sandwich?

-Ooh.

Oh, my gosh.

That's a game changer.

-Yeah, next level.

Next level.

-That is.

You've game-changed the recipe.

Oh, yes.

[ Chuckles ] -Mm-hmm.

I've got to try this.

-Let us help you with dinner tonight.

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Plugrà -- from professional kitchens to your home.

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