heat brown sugar and milk in a saucepan over medium heat.
Bring to a boil for two minutes, stirring continuously.
Stir in butter until it is melted.
Add powdered sugar 1 cup at a time and whisk together until chunks are gone.
Frosting will thicken a bit while it cools.
If it is too thin, add more powdered sugar. If it is too thick, add more milk.
ENJOY!