In a medium saucepan, combine 1/2 cup packed brown sugar, 3 tablespoons butter, and 1 tablespoon milk. Heat over medium heat until butter melts, stirring occasionally. Remove from heat. Stir in 1 cup sifted powdered sugar and 1 teaspoon vanilla. (If glaze becomes too thick, stir in a few drops of hot water.) Makes 3/4 cup.