1 cup unsalted butter or margarine, room temperature (use vegetable shortening when pure white icing is needed)
1/2 cup milk, room temperature
1/4 teaspoon salt
2 teaspoons vanilla or other desired flavoring
2 pounds confectioners' sugar
Combine all the ingredients in large mixing bowl and mix at slow speed until smooth. If stiffer icing is needed, or if the weather is very warm, add a little extra sugar. This recipe is enough to cover and fill a 9- by 13-inch sheet cake or two 9-inch layers.