1 cup unsalted butter (2 sticks), softened, but not melted
3 - 4 cups confectioners (powdered) sugar, sifted
1/4 teaspoon salt
1 tablespoon vanilla extract
up to 4 tablespoons milk or heavy cream
Beat butter for a few minutes with the paddle attachment of an electric mixer on medium speed. Add 3 cups of powdered sugar, turn mixer on lowest speed (so sugar doesn't blow every where) until the sugar has been incorporated with the butter. Increase mixer speed to medium and add vanilla extract, salt, and 2 tablespoons of milk/cream and beat for 3 minutes. If frosting needs a more stiff consistency, add remaining sugar. If frosting needs to be thinned out, add remaining milk/cream 1 tablespoon at a time.