These are good with or without the frosting.
Preheat oven to 375°.
Grease and flour, or line with parchment paper a 10X15 Jelly roll pan or a 9X13 baking pan for thicker bars (add 10 minutes to baking time if you use the 9X13 pan).
Whisk together the flour, baking soda and salt and set aside.
Beat the sugar, sour cream, softened butter and eggs until smooth and creamy.
Blend in the bananas and vanilla and beat for an additional minute.
Add the dry ingredients and blend for one minute.
Stir in nuts and spread in pan.
Bake 20 to 25 minutes (or 30-35 if using the 9X13 pan), until golden brown.
Cool slightly until warm, but not hot and frost with the Brown Butter Frosting.
Chef's notes: You can also use cream cheese frosting, just allow the bars to cool completely before icing.