American-style buttercream, made by beating butter with powdered sugar and a little milk, is one of the easiest types of frosting to make, but it tends to be cloyingly sweet, with a noticeable granularity from the sugar. This 1-2-3 formula—1 cup cream, 2 sticks of butter and 3 cups of powdered sugar—is nearly as simple and failsafe, but the cream, beaten in at the end, yields a more elegant frosting with a lighter flavor and fluffier, more supple texture. If you like, replace the vanilla extract with a tablespoon of grated lemon or orange zest, or make the chocolate variation below. Note that the recipe calls for the paddle attachment, not the whisk, as the frosting may wind up with too many air bubbles if whisked, making it difficult to achieve a smooth, satiny appearance when icing the cake.