This is the vanilla buttercream frosting printed on the back of WIlliams Sonoma's cupcake mixes. Made this and found it to be very simple, yet wonderful. Perfect for generously frosting a dozen cupcakes!
In the bowl of an electric mixer fitted with the flat beater, beat together the confectioners' sugar, butter, the 2 tablespoons milk, the vanilla and salt on low speed until combined, about 1 minute. Stop the mixer and scrape down the sides of the bowl. Increase the speed to medium and beat until fluffy, about 3 minutes. If the frosting is dry, add more milk, a tablespoon at a time, until it is creamy but still holds peaks.