In a mixing bowl, combine 1 lbs box of powdered sugar, 1/4 teaspoon salt, 1/4 cup milk, 1 teaspoon vanilla, and 1/3 cup soft butter or margarine.
Beat with electric mixer or heavy spoon until smooth and creamy, scraping bowl often. If too thick to spread easily, beat in a few drops of milk.
Frosts tops and sides of two 8 or 9-inch cake layers.
Servings: