How to change this frosting recipe to get a thicker result? Making chocolate cake and frosting per recipe below from Hershey's recipe. The frosting we made is a bit too liquidy to put on the cake, more like icing. is there a way (or even hack) to make it thicker, short of adding a cup of powdered sugar to cut the ratio of the liquid ingredients? 

"PERFECTLY CHOCOLATE" CHOCOLATE FROSTING
1/2 cup (1 stick) butter or margarine
2/3 cup HERSHEY'S Cocoa
3 cups powdered sugar
1/3 cup milk
1 teaspoon vanilla extract
Melt butter. Stir in cocoa. Alternately add powdered sugar and milk, beating to spreading consistency.


Add small amount of additional milk, if needed. Stir in vanilla. About 2 cups frosting.
Cream Cheese.

Whip in as much as you need to...

It won't be perfect Le Cordon Bleu, but it will be pretty good.

Bon Appetit