Recipe(tried): frosting for sugar cookies

I make sugar cookies and sell them. I have about 10 dozen to do this weekend here is the recipe I use.
Buttercream icing for cookies
1/2 cup crisco
1/2 cup butter, room temperature
1 tsp vanilla
4 cups powdered sugar
2 Tbs. cream, warm
Cream butter and shortening with electric mixer. Add vanilla. Gradually add sugar, one cup at a time, beating well on medium speed. Add milk and beat at high speed until light and fluffy. Keep covered until ready to use.
I put this in decorating bags with a star tip and decorate. Good luck