1 cup (2 sticks) unsalted butter, room temperature (or use half shortening and half butter)
1/3 cup brown sugar, packed
1 teaspoon ground cinnamon
1 teaspoon salt
4 cups powdered sugar
1 teaspoon vanilla (or to taste)
1 to 4 tablespoons heavy cream or milk
In a large mixing bowl, cream together the butter and brown sugar.
Beat in the ground cinnamon and salt. Beat in the powdered sugar slowly, adding the cream gradually.
If frosting is too thick, add a small amount of cream until desired consistency is achieved. If frosting is not thick enough, add powdered sugar until desired consistency is achieved. Humidity plays a huge part in the frosting consistency, so you may need to add more or less liquid, depending on humidity.