American-style buttercream, made by beating butter with powdered sugar and a little milk, is one of the easiest frostings 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 butter and 3 cups 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. A stand mixer works best, as it frees up both your hands, making it easier to gradually add the sugar and cream, but a hand mixer gets the job done, too. If you like, replace the vanilla extract with a tablespoon of grated lemon or orange zest, or make the chocolate variation below. The recipe makes enough to fill and frost an 8- or 9-inch two-layer cake, with an additional cup or so for piping and decorating. If you wish to store the frosting or have some leftover that you’d like to save for another dessert, refrigerate it in a microwave-safe container for up to three days. To soften it for use, microwave at 50 percent power, checking every 15 to 20 seconds, until just soft enough to easily stir, then whisk until smooth, creamy and spreadable.