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.