Step 1: Prepare the Batter

Preheat the oven to 375°F (190°C). Grease a 9×13-inch baking pan.

In a large bowl, mix sugar, sour cream, softened butter, and eggs until smooth.

Add mashed bananas and vanilla extract to the mixture. Stir until combined.

Gradually mix in flour, baking soda, and salt. If using walnuts, fold them in at this stage.

Step 2: Bake the Brownies

Pour the batter into the prepared baking pan, spreading it evenly.

Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.

Remove from the oven and let the brownies cool completely before frosting.

Step 3: Make the Frosting

Melt the butter in a saucepan over medium heat until it turns golden brown, stirring occasionally. Remove from heat and let it cool slightly.

Combine the browned butter with powdered sugar, vanilla extract, and milk in a mixing bowl. Beat until smooth and creamy.

Step 4: Frost and Serve

Spread the frosting evenly over the cooled brownies.

Slice into squares and enjoy!