(Thanks to Naree for taking pictures!)
Lemony White Cake
3 cups flour
3 teaspoons baking powder
1/4 teaspoon salt
1 cup (2 sticks) unsalted butter, softened
2 1/4 cup sugar
3 teaspoons vanilla extract
3 teaspoons lemon zest
9 large egg whites
1 cup milk
Red and blue food coloring (I used Wilton's icing colors)
Preheat oven to 350 degrees. Grease three 9-inch round cake pans and line the bottom with wax paper.
Combine flour, baking powder, and salt in a bowl. Mix well. In another bowl, whisk milk and egg whites until combined (don't use an electric mixer).
Cream butter and sugar on medium speed until soft and fluffy. Beat in vanilla and lemon zest. Reduce speed to low, and beat in 1/4 of the flour mixture, then 1/3 of the milk mixture in alternating batches, ending with the last of the flour mixture. Scrape down the bowl and beaters after each addition. When batter is combined, transfer 1/3 of the cake batter directly into the cake pan. Transfer 1/3 of the cake batter to another bowl and dye it blue. Dye the remaining cake batter red. Pour the dyed batter into their pans.
Bake for 30-35 minutes. Cool layers for 5 minutes, then unmold to finish cooling right side up. While cooling, make the frosting:
Coconut Buttercream Frosting
1 cup butter, room temperature
1/2 cup coconut milk
1 teaspoon vanilla extract
7 - 8 cups powdered sugar
Beat the butter until light and fluffy. Beat in 1/2 cup of the powdered sugar. When smooth, add the coconut milk, vanilla extract, and 1 cup of powdered sugar. Beat until smooth. Slowly add the rest of the powdered sugar, until the frosting reaches your desired consistency.
To assemble the cake:
(It's a bit difficult to explain in words, so if this doesn't make sense, check out this video of Elissa from 17 and Baking. She does a great job of explaining everything.)
When the cake layers have cooled, level the top of each cake layer. Split the red and white layers into two layers. Do not split the blue layer. Set one layer of each the red and white cake on top of the blue cake. Using a bowl or stencil, cut a circle into the three layers of cake. You want the outer ring to be about 2 inches wide. Save the outer ring of the blue cake and the inner circles of the red and white cake - the rest are scraps.
Set the large white cake circle on your cake stand/serving surface. Surround the cake with scraps of wax paper, sticking it a little under the cake. Spread a thin layer of frosting on the top of both the large and small white cake circles, spreading it all the way to the edges. Set the large red cake circle on top of the large white cake circle, and the small red cake on the small white cake. Spread another layer of frosting on the large red cake layer. Set the blue cake ring on top of the large cake layers. Frost the inside of the ring. Set the small cake layers inside the blue cake ring.
Frost the entire cake with a thin layer of frosting. This is your crumb coat, so it's okay if crumbs get caught in the frosting. Just make sure that every part of the cake is covered, so that crumbs don't get in your final coat. Chill the cake in the refrigerator for a half hour. Frost the cake again with its final coat of frosting. Slip out the pieces of wax paper for a clean presentation.