1 1/2 cups sugar
1 cup sour cream
1/2 cup butter, softened
1 3/4 cups ripe bananas, mashed, about 3 to 4
2 teaspoon vanilla extract
2 cups all purpose flour
1 teaspoon baking soda
3/4 teaspoon salt
1/2 cup chopped walnuts (optional)
brown butter frosting:
1/2 cups butter
4 cups powdered sugar
1 1/2 teaspoon vanilla extract
3 tablespoon milk
heat oven to 375°f. 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.
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).