Vanilla Sponge Cake
- Unsalted butter, for pan
- 1/2 cup all-purpose flour, plus more for pan
- 1/2 cup cornstarch
- 4 large eggs, separated
- 1 teaspoon pure vanilla extract
- 3/4 cup sugar
- Pinch of salt
Heat oven to 350 degrees. Butter a 9-inch-square baking pan. Line pan with parchment paper, and butter again. Flour the pan, and set aside. In a small bowl, sift together flour and cornstarch; set aside.
In the bowl of an electric mixer fitted with the whisk attachment, beat egg yolks, vanilla, and 1/2 cup sugar on high speed until thick and pale, about 5 minutes. Transfer the egg-yolk mixture to a large bowl. Wash and dry the mixer bowl and the whisk attachment.
Combine egg whites and salt in the mixer bowl, and beat on medium speed until whites hold soft peaks, about 1 1/2 minutes. With mixer running, slowly add the remaining 1/4 cup sugar. Continue beating until stiff and glossy, about 1 minute.
Fold the egg-white mixture into the egg-yolk mixture. In three additions, fold the reserved flour mixture into this new mixture. Transfer the batter to prepared pan, and smooth the top with an offset spatula. Bake until a cake tester inserted into middle comes out clean, 35 to 40 minutes. Transfer pan to a wire rack to cool; turn out cake, and wrap it in plastic wrap until ready to use.