Heat oven to 375º
Grease and flour 15X10 jelly roll pan
In a large bowl beat together sugar, sour cream, butter and eggs
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 20-25 minutes until golden brown.
BROWN BUTTER ICING
Heat butter in 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.
Wisk together until smooth. (it should be thinker 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)