• Preheat your oven to 375°F and prepare a 13 x 9 inch baking pan by greasing it.

For Brownies:

• In a large mixing bowl, beat together the sugar, sour cream, softened butter, and eggs until smooth and creamy.
• Incorporate the mashed bananas and vanilla extract into the mixture.
• Sift in the flour, baking soda, and salt, then mix for about a minute. Finally, fold in the chopped walnuts.
• Pour the batter into the prepared baking pan and spread evenly. Bake for approximately 25 minutes, or until the top is golden brown.
• Allow the brownies to cool slightly (they should be warm but not hot) before applying the frosting.

For Frosting:

• In a large saucepan over medium heat, melt the butter and keep a close eye on it. Once it reaches a medium brown hue, remove it from the heat.
• Gradually whisk in the powdered sugar one cup at a time, adding milk as necessary to achieve a smooth consistency. Finally, mix in the vanilla extract.
• Immediately pour the warm frosting over the brownies and smooth it out with a spatula or knife.
• Let the brownies cool completely before cutting them into squares.