1-1/2 c. sugar
1 c. sour cream
1/2 c. butter, softened
2 eggs
1-3/4 (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

1. Heat oven to 375F. Grease and flour 15×10-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.
2. Spread batter evenly into pan. Bake 20 to 25 minutes or until golden brown.
3. 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.
4. 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).