Melt butter in pan on top of stove over medium low heat.
Add brown sugar and milk.
Boil over low heat for 2 minutes, stirring all the time.
Remove, cool (just to luke warm and if it gets to thick you can place it back on the stove for a few minutes). I set the pan in a larger pan of cold water, stirring every 5 minutes, to cool it faster if I am in a hurry.
Add vanilla and powdered sugar. Beat well with hand mixer and frost cake.
Will frost a 9x13-inch cake.
If you want a thicker frosting then double this recipe if you are making a layer cake.
This is the icing we use on the Autumn Surprise cake, but is good on about any cake you can think of.