The Warm-Method Sponge Technique

To prepare the eggs for optimum foaming capacity when making all kinds of génoise, I use a bain-marie, or water bath—a technique of first warming the eggs and sugar to a temperature no higher than 100 degrees, then whipping them. This technique is called the warm-method sponge.

Though you can whip your eggs and sugar to the desired volume without using the warm method, my recipes are designed for this technique because it ensures that every time you make a génoise you will have begun with eggs at their proper temperature. Everything else will fall into place: Your sugar will dissolve, thereby uniting it with the eggs into a solution. Then the eggs will whip to their maximum volume faster, and their warmth will soften the natural fat (lecithin) in the yolk, surrounding the air cells and stabilizing the volume.