• 1 stick butter, melted
• 1 cup dark brown sugar
• 1/4 cup whole milk
• 3 1/4 cups sifted powdered sugar

Stir the sugar into the melted butter.  Bring to a boil, stirring, and boil for 1 minutes.

Remove from the heat and stir in the milk.  Beat until smooth.

Stir in the sugar.

Spread on cake while still warm.