Preheat an oven to 375°F and prepare a 9 X 13 pan by spraying with baking spray or lightly greasing.

Combine 1/2 cup of butter, white sugar, and brown sugar in a large bowl and mix until well combined.

Add the eggs, one at a time, mixing well between additions. Scrape the bowl as needed.

Add the vanilla and sour cream and beat until completely combined.

Add the bananas and mix until smooth.

Pour the batter into the prepared pan and bake for 25 to 30 minutes or until a toothpick inserted into the center of the brownies comes out clean.

During the last 5 minutes of baking, prepare the frosting.

Place 1/2 of butter into a medium sauce pan and set the heat to medium-high. Heat the butter until it starts to bubble, stirring frequently until the butter has turned a medium to dark blonde color, about 2 to 3 minutes. Turn off the heat.

Add the powdered sugar and mix to combine, add the vanilla and milk and stir until smooth and creamy.

Add more milk if the frosting is too thick.

Top the brownies with the frosting while the brownies and the frosting are still warm, this will make coating the brownies easier.