1-Preheat oven: Preheat oven to 350°F and grease an 11×15-inch jelly roll pan to prevent sticking.

2-Brown butter: Brown a total of 1 1/4 cups butter over medium heat until it turns light amber, then set aside 1/2 cup of the browned butter for the bars; don’t forget to scrape all those flavorful bits in for extra taste.

3-Refrigerate butter: Place the remaining browned butter in a bowl, stir in the additional 2 tablespoons chilled butter, and refrigerate it to solidify, which helps with the frosting later.

4-Whisk sugars: To the reserved 1/2 cup browned butter, whisk in the granulated and brown sugars until well combined.

5-Add wet ingredients: Add the eggs, then mix in the sour cream, mashed banana, and vanilla extract, whisking everything thoroughly for a smooth batter.

6-Add dry ingredients: Whisk in the baking soda and salt, then fold in the flour until just combined to keep the bars tender and avoid density.

7-Bake batter: Pour the batter into the prepared pan and bake for 25 to 30 minutes, or until a toothpick comes out clean.

8-Prepare frosting and spread: Cool slightly, then for the frosting, whisk the chilled browned butter gradually with powdered sugar, vanilla, and milk until smooth, and spread it over the warm bars.

9-Cool bars: Allow the bars to cool at room temperature for 30 minutes before slicing for the best texture.