Why are butter and eggs necessary in cakes?
Corriher: Butter has three roles in cakes: to make the cake light and delicate by holding air bubbles produced by leaveners like baking powder or soda; to make the cake tender by coating the flour protein; and to carry rich flavors. Stick margarine and shortening can substitute for butter; in fact, shortening is already aerated before you buy it, so it can produce a fine, tender cake. A margarine spread that is soft at room temperature can’t substitute for butter, though. Eggs have two parts, whites and yolks, which do two different things. Whites are an incredible drying and leavening agent, and yolks are nature’s great emulsifiers for creamy texture.
