To brown butter, heat unsalted butter in a light color saucepan over medium heat. Once the butter melts, it will become foamy. When the foam subsides, you will see clear bubbles, start whisking continuously at this point to keep the milk solids from burning. When the butter is caramel in color and smells nutty, turn off the heat and set aside to cool. This will take approximately 8 minutes and 30 seconds.

Preheat the oven to 350°F.

Brush a loaf pan with some melted butter and line the bottom with a piece of parchment paper, letting the excess hang over the sides. Brush the parchment paper with more butter. Set aside.

Mash the bananas with a potato masher in a large mixing bowl and add the cooled brown butter to it. Whisk together to combine.

Add brown sugar, eggs, vanilla, and beat until smooth.

Sift flour, baking soda, and baking powder into a small mixing bowl. Stir in the kosher salt. Add the flour mixture to the liquid mixture and fold until just combined.

Transfer the batter to the prepared loaf pan and bake for 55 minutes until a toothpick inserted in the center of the loaf comes out clean with just a few crumbs attached.

Allow the bread to cool in the pan for 10 minutes before removing it from the pan and let it cool further on a wire rack.