Brown Sugar Frosting

Melt butter in medium-sized, heavy saucepan over medium heat. When butter is melted, stir in brown sugar, reduce heat to low, and cook until sugar melts and begins to get slightly ropy, about 2 minutes, stirring occasionally. Stir in milk and raise heat to medium. Cook just until the mixture comes to a boil, stirring frequently. Remove pan from heat and cool to lukewarm. Either transfer misture to medium-sized mixing bowl or leave in saucepan if it is large enought. Add confectioner's sugar to the mixture, about 1/2 cup at a time, whicking vigorously until smooth and spreadable. Whisk in vanilla extract and use immediately.