This one is off of Martha Stewart's website. I trust her, don't you? Be careful not to deflate the whites!!! Learn how to fold if you don't know how already.
Makes one 9-inch by 13-inch cake.
* 1 1/4 cups (2 1/2 sticks) unsalted butter, room temperature, plus more for pan
* 4 1/2 cups sifted cake flour (not self-rising), 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
1. Preheat oven to 350 degrees. Butter a 9-by-13-by-2-inch baking pan. Line bottom with parchment or waxed paper. Butter paper; dust with flour. Tap out excess; set aside.
2. Sift together flour, baking powder, and salt into a medium bowl, and set aside. Combine milk and vanilla in another bowl; set aside. Place butter in a mixing bowl; using an electric mixer, beat until pale and creamy. Add sugar in a steady stream; continue beating until mixture is light and fluffy, about 3 minutes.
3. Reduce speed to low. Add flour mixture in three batches, alternating with milk mixture and starting and ending with flour; beat just until combined. Do not overbeat.
4. In another mixing bowl, beat egg whites until stiff peaks form. Fold one-third of the whites into the batter just until combined. Fold in remaining whites in two batches.
5. Pour batter into prepared pan; smooth top with a spatula. Bake until a cake tester inserted near the center comes out clean and the cake springs back when pressed lightly in the center, 35 to 45 minutes.
6. Transfer to a wire rack; let cool in pan at least 15 minutes. Run a paring knife around sides to loosen; invert cake onto rack. Remove paper; reinvert cake to prevent splitting. Let cool completely.
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