Cake can be made ahead and stored up to one day in refrigerator or up to one week in the freezer.
- 1 1/4 cups (2 1/2 sticks) unsalted butter, softened, plus more for pan and wire rack
- 4 1/2 cups sifted cake flour, plus more for pan
- 2 tablespoons baking powder
- 3/4 teaspoon salt
- 1 1/2 cups milk
- 1 1/2 tablespoons pure vanilla extract
- 2 1/4 cups sugar
- 7 large egg whites
Preheat oven to 350 degrees. Butter baking pan. Line bottom with parchment paper; butter paper, and dust with flour, tapping out any excess. Set aside.
Sift together flour, baking powder, and salt into a medium bowl, and set aside. Combine milk and vanilla in another bowl, and set aside. Beat butter in the bowl of an electric mixture fitted with the paddle attachment until pale and creamy. Add sugar in a steady stream, and continue beating until light and fluffy, about 3 minutes. Reduce speed to low. Add dry ingredients in three batches, alternating with the milk mixture and starting and ending with the dry ingredients. Be careful to avoid overbeating. Set aside.
In a clean bowl of an electric mixer fitted with the whisk attachment, beat egg whites until stiff peaks form. Fold a third of the whites into batter until combined. Fold in remaining whites in two batches.
Pour batter into prepared pan, and smooth top with a metal spatula. Bake until a tester inserted near the center comes out clean and the cake springs back when pressed lightly in the center, 35 to 45 minutes. Transfer to wire rack; cool 15 minutes before unmolding. Butter wire rack. Loosen cake sides with a paring knife, and invert cake onto greased rack. Reinvert to prevent it from splitting. Cool completely before using or storing in the freezer.