When we first started planning Evelyn's pool party that we hosted last weekend, she was looking at Pinterest with me and saw a rainbow cake. And that was when she decided she had to have one of those and I got a little scared.
I've watching hundreds of online tutorials. I've practiced on about 500 cakes in my life. I just can't do it. But I'll do anything for my little princess. So I set out to do it. Starting with researching the best method to do this.
All roads to rainbow cake seem to lead to Martha Stewart. Whether she was the first the showcase such a thing or what, it seems like every food blogger making a rainbow cake was talking about Martha Stewart's rainbow cake. Unfortunately, a lot of people were talking about how dry and uninteresting it is. Then I remembered that Rosie at Sweetapolita made a rainbow doodle cake for her daughter at one point, so I checked to see if it was Martha's version, and it was. (But not really, because it's really Whisk Kid's recipe that Martha features it on her website.) I really trust Rosie so I went with it. And I honestly have no idea why anyone complains about this cake. It's amazing. One of the best white (not really) cake recipes I've ever tasted.
This cake can be whatever color you want it to be, or just white. It called for 5 egg whites. Which is a lot, but was totally fine because I've been obsessed with using my ice cream maker and a lot of ice cream recipes call for egg yolks. Rosie recommended dividing the batter up by weight, but my kitchen scale is broken. So I measured the batter at 7.5 cups and realized that I had enough for 1 1/4 cups of batter for each layer. I broke it out into separate bowls and got to coloring. I have two 9" cake pans to my name, so I baked them two colors at a time, then changed out the parchment paper and threw two new colors into the pan. Even though the cake was baked in 6 thin layers, it was moist and delicious with the right amount of crumb.
I made the cake the Sunday before the party. I had the time before our week got crazy and when the cake layers cooled, I stacked them up with their parchment paper between them. Then, I wrapped them well in plastic wrap and popped them in the freezer. On Saturday morning, I took them out and let them defrost on the counter. When it was time to crumb coat, I carefully peeled the parchment paper rounds off the layers and got to stacking and icing.
As for the buttercream, I know I could have used any buttercream I wanted. But I wanted to try the one that came with the cake recipe because it was a lot of layers and the math on how much buttercream to make was already done. I didn't want to get half way through crumb coating the cake with my recipe only to realize that I didn't have enough. I loved the addition of lemon extract to the icing. It was a refreshing taste on a hot day. This may be the best Swiss Meringue buttercream I've ever had. And I may or may not have threatened to only make this buttercream from now on.
I was scared. I think overall it went well, but I won't go so far as to share my icing technique because I basically have none and its a crapshoot whether or not my cake will look cake shaped. I was very happy that this one had only a slight lean to it. The yellow layer cracked a little bit when I moved it to the cake stand, but it was not noticeable once the whole cake was assembled.
At party time, it was fun to reveal what was inside what looked like such a boring white cake. One dad was standing nearby and he said, "Our daughter's birthday is next month. I think you set the bar a little high." He jokingly thanked me and I assured him that if I could pull this off, I really think anyone can. The kids were thrilled and I was happy I didn't have to make an emergency trip to the bakery for a cake first thing in the morning.
Although I am not a fan of artificial food coloring, this cake was delicious. I can't wait to make it again with no food coloring (or natural colorings). The cake can be whatever color. The buttercream can use lemon extract or vanilla extract or whatever the occasion calls for. I have a feeling it won't be the last time I make a rainbow cake, though.
Rainbow Layer Cake
recipe courtesy of Sweetapolita, originally via Whisk Kid
3 cups all purpose flour
4 teaspoons baking powder
1/2 teaspoon salt
2 sticks unsalted butter, room temperature
2 1/3 cups sugar
5 egg whites, room temperature
2 teaspoons vanilla extract
1 1/2 cups milk, warmed in microwave for 30 seconds
Gel food coloring, not liquid
Preheat the oven to 350 degrees F. Grease as many 9" cake pans as you have and line with parchment paper. Have extra rounds of parchment ready to go if you don't actually have six 9" pans.
Sift the flour, baking powder and salt, then set aside.
Cream the butter and sugar. Then add the egg whites a little at a time. Add the vanilla and mix until incorporated. Alternating between wet and dry ingredients, add the milk and flour mixture in two parts.
Divide the batter among 6 bowls (I did 1 1/4 cup of batter per bowl), then whisk enough food color into each bowl to create the color you need. I only had 4 food colors, so I mixed colors to make orange and purple. The color of the unbaked batter is the color of the baked batter. Pour into prepared pans and bake for 10-15 minutes. (Mine baked for 12 minutes.)
Remove them from the oven and allow them to rest for 10 minutes before flipping them out of the pan and reusing the pan for the rest of the layers. Repeat until all layers are completed.
If icing the same day, allow the cake to cool completely before icing.
Lemon Swiss Meringue Buttercream
*This recipe called for two batches. One for filling and crumbcoating. And a 2nd half batch for icing. I only used the first batch for the whole thing. Again, I don't know the first thing about how to properly ice a cake, so someone who knows better than me might think its an insanely small amount of icing. But I thought it was just the right amount. Make this batch. If you need more, make more. Don't say I didn't warn you.
9 egg whites
1 3/4 cups sugar
4 sticks butter, room temperature, cut into 1 tablespoon pieces
2 teaspoons lemon extract
Cook the egg whites and sugar in a small saucepan over medium heat, whisking constantly until the sugar is completely dissolved (test by rubbing some between your fingers. If its completely smooth, it's done.) Pour into the bowl of your stand mixer and whip on high speed until room temperature. Then on medium-slow speed, add the butter, waiting until each piece is completely incorporated before adding the next piece. After all the butter has been added , turn the mixer back to high speed and whip until it has completely come together, about 5 minutes. Add the extract and beat to combine.