Jen, This is one that I posted before under the title Wilton Whipped Buttercream Frosting but it is very good. It is not a copycat as the recipe was with a Wilton Cake pan that I bought many years ago.

Wilton Whipped Buttercream Icing

The thick but creamy texture of this flavorful icing makes it ideal for decorating. It can be refrigerated in an airtight container for up to a week. Rewhip before using. Makes 2 cups.
Recipe may be doubled to make 4 cups, if a large or heavy duty mixer is used.

1/3 cup Solid Vegetable Shortening (Crisco)
1/3 cup Butter or Margarine*
1/4 teaspoon Vanilla
3 cups sifted Confectioners' Sugar (icing sugar)
(There are 4 cups in a pound)
1 Tablespoon + 1 teaspoon Milk

In a large mixing bowl; cream butter 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 the sugar has been mixed in, icing will appear dry. Add milk and beat at high speed until light and fluffy. Keep icing covered with a damp cloth until you're ready to decorate. For best results, keep icing bowl in refrigerator when not in use. (I cover it with plastic wrap)
*Restaurants and Stores usually use margarine but I have often used butter.
Enjoy! Judy