The many types of sponge cake have one characteristic in common: They are made with an egg foam that contains yolks. These are usually whole-egg foams but, in some cases, the base foam is a yolk foam and an egg white foam is folded in at the end of the procedure.
In its simplest form, sponge cake batter is made in two basic steps: (1) eggs and sugar are whipped to a thick foam, and (2) sifted flour is folded in. Additional ingredients, such as butter or liquid, complicate the procedure slightly. It would be too confusing to try to include all the variations in one procedure, so instead we describe four separate procedures.