Single 8-Inch White Cake Round
Makes one 8-inch cake layer
If you’ve forgotten to bring the milk and the egg whites to room temperature, set the bottom of the measuring cup containing the mixture in a bowl of hot water and stir until the mixture feels cool rather than cold, about 65 degrees. The cake can be wrapped and stored for 24 hours.
1. Adjust oven rack to middle position and heat oven to 350 degrees. Grease and flour 8-inch round cake pan. Combine milk, egg whites, and vanilla in 2-cup liquid measuring cup.
2. Using stand mixer fitted with paddle, mix flour, sugar, baking powder, and salt on low speed until combined, about 30 seconds. Add butter and continue to mix until mixture resembles moist crumbs, with no powdery streaks remaining, about 1 minute. Add half of milk mixture, increase speed to medium, and beat until smooth, about 1½ minutes, scraping down bowl as needed. With mixer running, add remaining milk mixture and beat until fully incorporated, about 30 seconds.
3. Pour batter into prepared pan and spread into even layer with rubber spatula. Bake until toothpick inserted in center comes out clean, 21 to 25 minutes, rotating pan halfway through baking.
4. Let cake cool in pan for 5 minutes, then loosen from sides of pan with butter knife. Invert onto large plate, then reinvert onto wire rack. Let cool completely, about 1½ hours.