1 pound unsalted butter, softened
1/4 teaspoon table salt
3 to 4 tablespoons skim milk
2 teaspoons quality vanilla extract
1 3/4 pounds powdered sugar (sift if there are any lumps)
When making this recipe for cakes with a buttercream finish, it is best to double it. This will make a batch of icing that completely fills a 5-quart mixer bowl. A double batch should fill the bowl beyond the beater, leaving your resulting icing smooth and fairly free of air bubbles. Adding the liquids before the sugar and mixing only on a low speed prevents the formation of pesky air bubbles that cause problems when trying to frost a buttercream cake smoothly. It is important to mix the icing for the full 10 minutes in the final step. However, if you would prefer a fluffier aerated icing for cupcakes or cakes you can simply raise the mixer speed to medium and beat the icing for 4 to 5 minutes. In warm weather, when piping flowers or peaked designs, consider replacing 25 percent of the butter with a quality shortening, such as Crisco.