Melt butter in saucepan.
Stir in brown sugar.
Heat to boiling, stirring constantly.
Boil and stir over low heat 2 minutes.
Stir in milk; heat to boiling.
Remove from heat and cool to lukewarm.
Gradually stir in confectioners' sugar.
Place pan of frosting in bowl of ice and water; beat until spreading consistency.
If frosting becomes too stiff, heat slightly, stirring constantly.