Because of the shortening, the icing sets up nicely after a little while and you can safely stack the cookies for easy transport or storage without mashing the frosting on the bottom cookie.
4 c. confectioners' sugar
1/2 c. shortening
5 Tbsp. milk
1 tsp. vanilla extract
food coloring, optional
1. In a large mixing bowl whip the shortening until fluffy. Add the shortening 1 cup at a time until smooth and well incorporated. Add the milk and extract, mixing until combined. If desired, add the food coloring.
I doubled the batch and had enough frosting for 67 1 1/2" round sugar cookies, with about 2 cups leftover.