Buttercream Icing

Cream margarine and shortening with electric mixer. Add vanilla. Gradually add sugar, one cup at a time, beating well on medium speed. Scrape sides and bottom of bowl often. When all sugar had been mixed in, icing will appear dry. Add milk and beat at medium speed until light and fluffy. To thin for icing cake, add a small amount of light corn syrup. (I think that the corn syrup makes it too sickeningly sweet--I thin it with a little milk with great success.) Can be kept refrigerated in an airtight container for up to two weeks.