The brown butter icing was nasty sweet! That being said I am not an icing fan and even less fan of powdered sugar icing.
1/2 C butter ( I use unsalted)
4 C powered sugar
1 1/2 tsp vanilla
3 TBSP milk
Brown butter in saucepan (it will turn dark and smell nutty) remove from heat.
Add powdered sugar, vanilla , and milk. Whisk together until smooth (thicker than glaze thinner than frosting).
I pinned this recipe on my RECIPE board on Pinterest if you are interested in the recipe in its entirety. Banana Bread Bars-Brown Butter Frosting
This recipe made a jellyroll pan full. I could have used 1/2 the icing IMO.