In the bowl of an electric mixer, beat together shortening and butter or margarine until light and fluffy. Beat in vanilla.
With the mixer on medium speed, add in confectioners’ sugar, 1 cup at a time. Gradually add in milk and beat until light and fluffy. Beat in food coloring if using.
Recipe by Between Carpools at https://betweencarpools.com/ice-cupcake-make-kid-super-happy/