1Place the butter in the bowl of a stand mixer fitted with a paddle attachment and beat on medium speed until light and fluffy, about 2 minutes. Stop the mixer and scrape down the beater and sides of the bowl with a rubber spatula.
2Turn the mixer to medium low, gradually add the powdered sugar, and beat until combined, about 2 minutes.
3Add the remaining ingredients and beat until the frosting is very airy and thoroughly mixed, about 2 minutes. Use immediately to frost cookies or cupcakes, or store covered in the refrigerator until ready to use.