Warm-Method Sponge Cake

Many fancy tortes start with classic sponge cake. For a soft, flexible cake that will be flavored with a soaking liquid or can be baked in a jelly-roll pan to make a roulade, the whole eggs and sugar are heated over hot water until very hot. Most recipes use a six-egg batter, but some require the four- or eight-egg recipes, which follow.

Some sponge cake recipes skip butter altogether, but I use a small amount to add flavor and a bit of extra firmness (but not so much that it harden