Simple buttercream icing is typically flavored with vanilla extract to add something beyond the sugar and butter flavors, but the vanilla extract can be omitted or substituted for a different flavor. You can still use the icing to top cakes, cupcakes, cookies and more. It might be best to omit flavorings altogether if you want don't want to compete with a flavorful cake, such as spice cake, but just want to enhance it with a sweet topping.
Whip softened butter with an electric mixer until creamy. It takes 1 cup of butter to yield 3 cups of icing. While buttercream is widely used, icing doesn't have to include butter at all. Instead, you can skip the butter and make a thin, pourable icing that you might pour over homemade donuts or use for dipping French toast sticks.
Mix your choice of flavoring with the creamed butter, if desired, using about 1 teaspoon of a flavor extract, such as almond or lemon, to yield 3 cups of frosting. Mix in 1/4 cup of cocoa powder or 3 ounces of melted chocolate to make a chocolate buttercream icing. If you prefer, skip the flavoring altogether to make plain buttercream icing.
Add powdered sugar 1 cup at a time, and mix it well at medium speed until it is well-incorporated, thick and dry. You'll need 4 cups or about 1 pound of powdered sugar to yield 3 cups of frosting.
Mix in milk 1 tablespoon at a time at medium speed, using 2 to 4 tablespoons to yield 3 cups of icing. Mix the icing for about 5 minutes until it becomes light and fluffy. The amount of milk varies, so add 1 tablespoon at a time until soft peaks form. If you skipped the butter and plan to make thin, pourable icing, use even more milk until you achieve a thin consistency that easily drizzles from a spoon.