Preheat the oven to 350°F. Line 2 9-inch round cake pans with parchment paper. Set aside.
Place the egg whites in a large metal bowl, and place the egg yolks and vanilla in a smaller mixing bowl.
6 large eggs, 1 teaspoon pure vanilla extract
Add 1⁄2 cup granulated sugar to the bowl with the egg whites. Using a hand mixer, beat on low until foamy, then increase the speed gradually and beat until stiff peaks form, about 5 minutes. Add the remaining sugar to the bowl with the egg yolks. Beat until very thick and pale yellow.
1 cup granulated sugar
Carefully fold the egg yolk mixture into the whipped egg whites.
Fold the flour into the egg mixture in 3 additions until well mixed, being careful not to overmix. Divide batter evenly into the prepared pans. Bake for approximately 30 minutes, or until a toothpick inserted comes out dry.
1 cup cake flour
Transfer to a cooling rack, cool for 10 minutes, then remove cakes from pans to cool completely.
Fill with your favorite jam, cream, or curd, and serve with fresh berries and whipped cream, if desired.