Melt 1/2 cup butter. Stir in 1 cup packed brown sugar, boil and stir 2 minutes, stir in 1/4 cup milk, heat to boiling. Remove from heat and cool to lukewarm. Stir in 2 cups powdered sugar, beat until thick, dull and smooth. Enough frosting to cover a 9 x 13 inch cake. Add nuts on top of frosted cake; if you like.