- 3/4 cup all-purpose flour
- 3/4 cup cornstarch
- 6 large egg whites
- 6 large egg yolks
- 1 1/2 teaspoons vanilla extract
- 3/4 cup + 6 tablespoons sugar
- 1/4 teaspoon salt
- 2 cups unsalted butter, room temperature
- 1 teaspoon vanilla extract
- 5 cups confectioner's sugar
- Pink, orange, yellow, green, blue and purple food coloring
- Beat the egg yolks, vanilla extract and 3/4 cup sugar with an electric mixer on high speed until thick and pale. Set aside.
- In a separate bowl, beat the egg whites and salt with an electric mixer on medium speed until soft peaks form.
- Slowly add the remaining 6 tablespoons sugar and beat until stiff, glossy peaks form.
- Gently fold the egg white mixture into the egg yolk mixture.
- Combine the flour and cornstarch in a small bowl, then add to the egg mixture in 3 additions.
- Divide the mixture into 6 bowls and dye each bowl of batter a different color.
- Be sure to gently fold the food coloring in - you want to keep the batter as airy as possible.
- Pour the batter into 6 greased and floured 9-inch round cake pans.
- Bake at 350 degrees F for about 5 minutes, until the cakes are fully cooked.
- Transfer the cakes to a wire rack and allow them to fully cool.
- Using a plate as a stencil, cut the edges off each layer of cake. This will give the cake a clean look and make layering much easier.
- Place the purple layer of cake on a serving platter of your choice and spread some of the white buttercream evenly onto the surface. Place the blue layer of cake on top and top with some more buttercream. Continue in the order of the rainbow until you reach the pink layer. Spread a thin layer of the remaining white buttercream over the entire surface of the cake.
- Pipe rainbow stripes of buttercream onto the cake, starting with the base of the cake with the purple buttercream. Once you reach the pink buttercream, work backward in the order of the rainbow to create a pretty, rainbow ombre effect. Repeat until the cake is fully covered in buttercream and enjoy!
- Place the butter in a bowl and whip with an electric mixer until pale and fluffy.
- Add the vanilla extract and mix to combine.
- Add the confectioner's sugar one cup at a time, mixing well after each addition.
- Then whip for 3 to 5 minutes, until fluffy.
- Set a third of the buttercream aside.
- Divide the remaining buttercream into 6 bowls and dye them the colors of the rainbow.
- Place each color in a piping bag fitted with a star-shaped piping tip.