Fats

In the standard method for making pound and layer cakes, the cook beats fat and sugar together to incorporate air bubbles, until the mixture reaches the fluffy consistency of whipped cream. Solid fats retain air bubbles thanks to their semisolid consistency: the air carried along by the sugar crystals and beater becomes immobilized in the mixture of crystalline and liquid fat. Butter is the traditional cake fat, and is still the fat of choice for bakers who value flavor more than lightness of texture.