- 18 ounces cake flour, plus more for the pan
- 2 teaspoons baking powder
- 1 1/2 teaspoons baking soda
- 1 teaspoon salt
- 2 cups buttermilk
- 2 teaspoons vanilla extract
- 1/2 cup unsalted butter, room temperature
- 1/2 cup oil
- 2 cups granulated sugar
- 3 large egg whites
- 1 large egg yolk
- Preheat oven to 325°F. Butter or oil baking pan, line bottom of pan with parchment paper; butter paper and dust baking pan with flour, tapping out any excess. Set aside.
- Sift together flour, baking powder, baking soda, and salt into a medium bowl, and set aside.
- Combine buttermilk and vanilla in another bowl, and set aside.
- Beat butter, oil, and sugar in a bowl of an electric mixer fitted with the paddle attachment and cream until pale and fluffy, about 3 minutes.
- Reduce speed and add egg whites one at a time. Scraping down mixer bowl between each addition. Add egg yolk and mix until combined.
- Reduce speed to low. Add dry ingredients in three batches, alternating with the buttermilk mixture. Starting and ending with the dry ingredients. Be careful not to over mix the batter.
- Pour batter into prepared pan, and smooth top with a spatula. Bake at 325 degrees until a toothpick inserted near the center comes out clean and the cake springs back when pressed lightly in the center, about 30-40 minutes.
- Transfer to a wire rack to cool before unmolding.
- To unmold, run a knife around the edge of the cake to loosen cake sides, invert cake to release from pan. Cool completely before decorating.
2 8-inch rounds