Foolproof Sponge Cake(Cook'S Illustrated) - cooking recipe

Ingredients

1/2 cup cake flour
1/4 cup unbleached all-purpose flour
1 teaspoon baking powder
1/4 teaspoon table salt
3 tablespoons milk
2 tablespoons unsalted butter
1/2 teaspoon vanilla extract
5 eggs, room temperature
3/4 cup granulated sugar

Preparation

Adjust oven rack to lower middle position and heat oven to 350 degrees. Grease two 8- or 9-inch cake pans and cover pan bottoms with a round of parchment paper. Whisk flours, baking powder, and salt in a medium bowl (or sift onto waxed paper). Heat milk and butter in a small saucepan over low heat until butter melts. Remove from heat and add vanilla; cover and keep warm.
Separate three of the eggs, placing whites in bowl of standing mixer fitted with whisk attachment (or large mixing bowl if using hand mixer or whisk) and reserving the 3 yolks plus remaining 2 whole eggs in another mixing bowl. Beat the 3 whites on high speed (or whisk) until whites are foamy. Gradually add 6 tablespoons of the sugar; continue to beat whites to soft, moist peaks. (Do not over-beat.) If using a standing mixer, transfer egg whites to a large bowl and add yolk/whole egg mixture to mixing bowl.
Beat the 3 yolks & 2 whole egg mixture with remaining 6 tablespoons sugar. Beat on medium-high speed (setting 8 on a KitchenAid) until eggs are very thick and a pale yellow color, about 5 minutes (or 12 minutes by hand). Add beaten eggs to whites.
Sprinkle flour mixture over beaten eggs and whites; fold very gently 12 times with a large rubber spatula. Make a well in one side of batter and pour milk mixture into bowl. Continue folding until batter shows no trace of flour, and whites and whole eggs are evenly mixed, about 8 additional strokes.
Immediately pour batter into prepared baking pans; bake until cake tops are light brown and feel firm and spring back when touched, about 16 minutes for 9-inch cake pans and 20 minutes for 8-inch cake pans.
Immediately run a knife around pan perimeter to loosen cake. Cover pan with large plate. Using a towel, invert pan and remove pan from cake. Peel off parchment. Re-invert cake from plate onto rack, (see illustrations below). Repeat with remaining cake and continue with one of the related recipes.
Step-by-Step Folding Without Deflating: With spatula perpendicular to the batter, cut through the center down to the bottom of the bowl.
Holding the spatula blade flat against the bowl, scoop along bottom, then slide up the side of the bowl.
Fold over, lifting the spatula high so that the batter falls without the spatula pressing down the batter.