Cotton Sponge Cake | Light Cake Leavened with Whipped Egg Whites

Separate the eggs. Even a drop of yolk can keep the whites from whipping, so crack each egg into a separate bowl. Add the lemon juice to the whites and beat at medium speed, adding two-thirds of the sugar in three batches. Stop when lifting the whisk leaves soft peaks with tips that curl slightly.

Add one-third of the meringue to the mixture and whisk freely to loosen it. Add the remaining meringue in two batches, folding from the bottom up with a spatula. Finish in no more than twenty strokes; every extra stroke knocks air out of the foam.

Pour the batter into an ungreased tube pan and smooth the top with a spatula. Do not grease the pan: the batter climbs the sides as it bakes, and it cannot grip a greased surface to rise. Tap the pan lightly on the counter once.

Bake in an oven preheated to 160°C / 320°F for 40 minutes, and do not open the oven door during the first 30 minutes. This recipe uses 160°C / 320°F instead of the usual 175°C / 345°F; higher heat sets the surface too early, causing the cake to crack as it rises inside. It is done when the top springs back without leaving an indentation when pressed with a finger.