A butter cake is a cake in which one of the main ingreients is butter. These cakes are considered one of the quintessential cakes in American baking. They find their origins in the English pound cake, which traditionally used equal parts of butter, flour, sugar, and eggs to produce a heavy, rich cake. The invention of baking powder and other chemical leavening agents during the 19th century substantially increased the flexibility of this traditional pound cake by introducing the possibility of creating lighter, fluffier cakes using these traditional combinations of ingredients, and it is this transformation that brought about the modern butter cake.