1/2 c. butter
1 c. brown sugar, firmly packed
1/4 c. milk
1 3/4-2 c. sifted confectioners' sugar

Melt butter; add brown sugar and cook over low heat 2 minutes, stirring constantly. Add milk and continue stirring until mixture comes to a boil. Remove from heat and cool. Add confectioners' sugar until of right consistency to spread.