In large bowl, beat shortening and butter with electric mixer until light and fluffy. Beat in vanilla.
Gradually add 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 milk; beat at medium speed until light and fluffy.
For Pure White Icing (stiff consistency), omit butter; substitute an additional 1/2 cup shortening for butter and add 1/2 teaspoon No-Color Butter Flavor. Add up to 4 tablespoons light corn syrup, water or milk to thin for icing cakes.
Note: If using a hand mixer, beat shortening, butter, if used, and liquid first, then add sugar, as above. It may be necessary to add additional sugar for the correct consistency.
Makes about 2-1/4 cups of icing / Recipe courtesy of Wilton
Making the frosting and toppings Frozen-style
To get the blue tint for Frozen-themed cupcakes, add 8 drops of blue food coloring, stir it all in, and see how you like the color. Add more food coloring until you get the exact shade you want.