1. Heat butter over medium heat in a 2-quart saucepan.
2. When the butter is melted, stir in brown sugar.
3. Heat to boiling, stirring constantly.
4. Reduce heat to low and boil 2 minutes longer, still stirring.
5. Stir in milk and heat to boiling.
6. Remove from heat and cool.
7. Slowly stir in powdered sugar.
8. Place saucepan of frosting in a bowl of very cold water and beat frosting until smooth. If frosting is too stiff, add an additional 1 teaspoon of milk at a time until frosting is smooth.

Frosts one 9×13 inch cake.