Baker's Chocolate One Bowl Chocolate Frosting

I hate making frostings, but this is a rich tasting, easy recipe to make if you have 4 squares of unsweetened chocolate and a pound of powdered sugar on hand. The only problem that I have with this recipe is that they say to add the powdered sugar, butter and vanilla and then add the milk. If I do this I get concrete, so I don’t add all of the sugar at once. I then alternate adding it with the milk. It is important to end with the milk so it turns out glossy.