In large bowl, beat 1/2 cup shortening and 1/2 cup butter with electric mixer until light and fluffy. Beat in 1 teaspoon vanilla extract.
Gradually add 4 cups sifted powdered sugar, one cup at a time, beating well on medium speed. Scrape sides and bottom of bowl often. When all sugar has been mixed in, icing will appear dry.
Gradually add 2 tablespoons of milk; beat at medium speed until light and fluffy.