Pan di Spagna Sponge Cake

Ingredients

5 large eggs, room temperature
1 ½ cups sugar
1 ½ cups flour
1 tsp vanilla
½ tsp grated lemon peel
butter and flour for the pan
Directions

Separate the eggs putting the yolks in a large bowl and the whites in a smaller bowl. Add the sugar to the yolks, and beat until the consistency of frosting.
Beat the whites until they stand stiff.
Fold the whites into the yolk-sugar mixture. Turn it over slowly and gently until completely mixed.
Sift the flour (even if you don't usually sift flour--do it).
Fold the flour slowly, a bit at a time, to the egg-sugar mixture.
Add the vanilla and lemon peel, folding in gently.
Butter and flour a 9" cake pan. Pour in the batter and bake at 350F, for about 20 minutes. When done the cake will be toasty on top, and a toothpick will come out clean.
Turn upside down to cool. Let cool before frosting.