Banana Bread Bars with Brown Butter Frosting

 Banana Bread Bars:
1-1/2 c. sugar
1 c. sour cream
1/2 c. butter, softened
2 eggs
1-3/4 c. (3 or 4) ripe bananas, mashed
2 tsp. vanilla extract
2 c. all purpose flour
1 tsp. baking soda
3/4 tsp. salt
1/2 c. chopped walnuts (optional)

Brown Butter Frosting:
1/2 c. butter
4 c. powdered sugar
1-1/2 tsp. vanilla extract
3 tbsp. milk

How to make it :

Heat oven to 375F.  Grease and flour 15x10-inch jelly roll pan.  For the bars, in a large bowl, beat together sugar, sour cream, butter, and eggs until creamy.  Blend in bananas and vanilla extract.  Add flour, baking soda, salt, and blend for 1 minute.  Stir in walnuts.
Spread batter evenly into pan.  Bake 20 to 25 minutes or until golden brown.
Meanwhile, for frosting, heat butter in a large saucepan over medium heat until boiling.  Let the butter turn a delicate brown and remove from heat immediately.
 Add powdered sugar, vanilla extract and milk.  Whisk together until smooth (it should be thicker than a glaze but thinner than frosting).  Using a spatula, spread the brown butter frosting over the warm bars (the frosting will be easier to spread while the bars are still warm)