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 hardens when refrigerated). To give the butter more flavor, allow it to brown slightly during melting, and leave the milk solids behind in the saucepan when pouring it out.
Take care when folding the flour into the beaten eggs; the flour should be completely incorporated without lumping. The best folding utensil for sponge cake is a large balloon whisk with thin wires, used just like a spatula, allowing the batter and flour to flow through the wires. If you are using a heavy-duty mixer to beat the eggs (by far the best method), the whisk attachment can be detached and held to manually fold in the flour. A large rubber spatula is another option, but a whisk works best.
It is not always necessary to trim off the top crust of the cake. In some tortes, when the cake layers are going to be soaked with syrup, this crust can act as insulation to keep the syrup from seeping out. In this case, place the top cake layer, crust side down, in the pan being used for molding the torte.
The batter works equally well with either cake or all-purpose flour. Cake flour makes a slightly more tender cake.