Here is the buttercream recipe I use in my cake shop:
List of Ingredients
1 pound Butter
(do not substitute)
1 pound Crisco
2 pounds Powdered sugar
1/2 To 1 teaspoon vanilla
Recipe
Beat butter and shortening thoroughly. Add 1 pound powdered sugar and beat well. Add the flavoring and mix into icing. Add the remaining sugar. Beat for 3 to 4 minutes.