March is a big month for birthdays. So far I've celebrated the birthdays of two coworkers (with elaborate three-layer cakes), the birthdays of no fewer than four Facebook friends (with generic, "happy birthday so-and-so!!" messages) and the 100th birthday of the Oreo (with a late afternoon vending machine run, though if I had it to do over again I'd definitely be making these).
Let's leave aside the junk-food binges and virtual well-wishes for now and focus instead on the three-layer cakes. Specifically, this three-layer, homemade funfetti cake, which I made for my friend and coworker Katie's birthday. (The other birthday cake was the almond joy confection featured here.) The fun thing about this cake is that it looks like any other plain white cake from the outside--it's not until you slice it open that your guests realize what's hidden within.
I wanted a stark white cake to offset the brightly colored sprinkles, but was wary of ending up with something dry or cloyingly sweet. To that end, I made a riff on a favorite buttermilk cake and was extremely happy with the results. The cake was as scrumptious as it was stunning, and it will definitely be a part of my celebration cake rotation for many a birthday-packed March to come.
For the Cake (Adapted from Perfect Party Cake, Dorie Greenspan's Baking From My Home to Yours)
2 cups all purpose flour*
1 tablespoon baking powder
1/2 teaspoon salt
1 1/4 cups buttermilk
4 egg whites
1 1/2 cups sugar
1 stick unsalted butter, at room temperature
1/2 teaspoon vanilla extract
1/3 cup multi-colored sprinkles
*edited to note: The original recipe for the Perfect Party Cake calls for 2 1/4 cups cake flour. Since I didn't have any cake flour on hand, I substituted with a lesser amount of all-purpose flour. I haven't tested this version with cake flour, but it will likely produce a lighter cake with a more delicate crumb. If that's what you're after, it may be worth using 2 1/4 cups cake flour here instead of 2 cups of all-purpose.
For the Frosting
3 sticks unsalted butter, at room temperature
4 cups powdered sugar
1/2 teaspoon vanilla extract
pinch of salt (optional)
Preheat the oven to 350. Butter three 9-inch round cake pans and line the bottoms with parchment paper. Sift the flour, baking powder and salt into a bowl and set aside. In a separate bowl, stir together the egg whites and buttermilk and set aside as well. In the bowl of a stand-mixer fitted with the paddle attachment, beat the butter and sugar until light and fluffy,about three minutes. Beat in the vanilla extract. With the mixer running, add in 1/3 of the flour mixture, followed by 1/2 of the buttermilk mixture. Continue alternating the flour and milk, adding another 1/3 of the flour mixture, the remaining buttermilk, and then the rest of the flour. Scrape down the sides of the bowl if necessary, and then beat the batter on medium for about a minute to make sure it's well incorporated. Turn off the mixer, and gently stir in the sprinkles. Divide the batter between the prepared pans, and bake for about 30-35 minutes, or until the cake is golden, springy to the touch, and a tester inserted in the center of the cakes comes out clean. Allow the cakes to cool in the pans for about 10 minutes, then run a knife around the edges, invert onto wire racks, and peel off parchment paper. Allow the cakes to finish cooling completely.
To make the buttercream icing, beat the butter on medium speed for about 30 seconds, or until light and soft. Slowly beat in the powdered sugar. Once all of the sugar has been incorporated, add the vanilla extract, and a pinch of salt if desired. Beat on medium speed for another minute, or until the frosting is light and fluffy.
To assemble the cake, place one layer on a plate or cake board. Spread a thin layer of buttercream over the top of the cake. Place another cake layer on top, and repeat with another thin layer of frosting and the remaining cake layer. Working with an offset spatula if you have one, spread a very thin layer of icing over the top and sides of the cake, using a thicker coating of icing where needed to fill in any holes or gaps in the cake. This is your crumb coating--a very thin layer of icing in which all of the crumbs are suspended so that they're not visible in the finished cake. Once you have applied your crumb coating, pop the cake in the refrigerator or freezer for about 20 minutes to harden. Remove the cake from the refrigerator, and spread the rest of the icing in an even layer over the top and sides of the cake. Decorate with more sprinkles, if desired.