1-Combine the butter for the bars and frosting, totaling 1 1/4 cups, in a saucepan over medium heat and brown it until it reaches a light amber color for that rich taste.

2-Divide the browned butter: reserve 1/2 cup for the bars and pour the rest into a mixing bowl, then mix in the extra 2 tablespoons of butter and refrigerate it for the frosting later.

3-Pour the 1/2 cup of reserved browned butter into a separate bowl and whisk in the granulated sugar and brown sugar until well blended.

4-Whisk in the eggs, followed by the sour cream, mashed bananas, and vanilla extract to create a smooth batter base.

5-Add the baking soda and salt, then stir in the flour just until combined, avoiding over-mixing to keep the bars soft.

6-Pour the batter into your prepared pan, spread it evenly, and bake for 25-30 minutes or until a toothpick comes out clean.

7-While the bars cool, prepare the frosting by using the chilled brown butter and gradually whisking in powdered sugar one cup at a time, followed by vanilla and milk until smooth.

8-Spread the frosting over the slightly warm bars, let them cool for about 30 minutes, then slice and serve for the best flavor.