Génoise (sponge cake), the classic layer cake of France, is one of the cakes used most often in French pâtisserie, and is a component of many dessert preparations. It differs from the traditional American sponge cake, as well as the classic French biscuit, in that the eggs are heated and beaten whole rather than whipped separately. All sponge cakes rely on eggs for their light texture. No other leavening agent, such as baking soda or baking powder, is used to create the desired airiness. The cake rises as the heat of the oven causes the air in the batter to expand — the air that was trapped in the whipped eggs and the air produced as the water in the butter turns to steam. Although a properly made génoise is light and delicious on its own, the ways in which it can be decorated or finished are myriad. It particularly shines when brushed with a flavored syrup and layered with buttercream.