1/2 c. butter
1/4 c. milk
1 c. brown sugar, packed
3 1/2 c. powdered sugar, sifted
In saucepan melt margarine and stir in brown sugar. Cook and stir until bubbly.
Remove from heat and add milk. Beat vigorously until smooth.
Add powdered sugar and beat by hand until spreading consistency.
Frost cake immediately.