6 T. butter, softened
~3 cups powdered sugar
1/3 cup milk
1 t. vanilla
Mix it all together, adding more liquid or sugar depending on the consistency you want. Makes about 2 cups.
This is the same recipe as Homemade Chocolate Frosting, without the cocoa and adding a bit more sugar. I rarely measure the sugar and milk anyway, just mixing it until it's the consistency I want.