Instructions

• Preheat oven to 375°F. Grease and flour a 9×13-inch pan.
• In a large bowl, beat together 1½ cups sugar, 1 cup sour cream, ½ cup butter (softened), and 2 eggs until creamy and well combined.
• Stir in 3–4 ripe mashed bananas (about 2 cups) and 2 teaspoons vanilla extract until evenly mixed.
• Add 2 cups all-purpose flour, 1 teaspoon baking soda, and ¾ teaspoon salt; blend for about 1 minute or until just combined.
• Fold in ½ cup chopped walnuts, if using.
• Spread the batter evenly in the prepared 9×13 pan and smooth the top.
• Bake 20–25 minutes, or until the top is golden brown and a toothpick inserted into the center comes out with a few moist crumbs. Remove from oven.
• While the bars are baking or immediately after you remove them, make the frosting: in a small saucepan over medium heat, melt ½ cup butter and cook until it turns a light golden brown and smells nutty; remove from heat immediately.
• Whisk into the browned butter 4 cups powdered sugar, 1½ teaspoons vanilla extract, and 3 tablespoons milk until smooth and spreadable.
• Using a spatula, spread the brown-butter frosting over the warm bars (the frosting will spread more easily while the bars are still warm).
• Allow the frosting to set at room temperature, then cut into bars and serve.