• Preheat the oven to 350 degrees F. Prepare a 9x13 inch baking pan with cooking spray or parchment paper.

For the bars:

• Melt ½ cup butter (one stick) in a sauce pan over medium heat. Continue to cook, stirring occasionally until the butter smells nutty and is a light golden brown. It should be quite foamy at this point. Remove from the heat. Using a large bowl, add the browned butter, white sugar, and brown sugar. Whisk to combine. Be sure to use a heat proof bowl.
• Whisk in eggs, then add the sour cream, mashed bananas, and vanilla. Stir with a wooden spoon.
• In a separate bowl, add the flour, baking soda, and fine sea salt. Whisk to combine well.
• Gradually add the flour mixture to the butter mixture, stirring until just combined. A few spots of flour is ok, but be sure to scrape the bottom of the bowl to incorporate all the flour. Do not over mix.
• Pour batter into prepared pan. Bake in preheated oven for 25 to 30 minutes or until a toothpick inserted in the center comes out clean (or a few dry crumbs).

For the frosting:

• Add 4 tablespoons of butter to the same pan as before and brown the butter like you did for the bars. When the butter has browned, add the vanilla then the sifted powdered sugar. Stir well to remove any lumps. Add half and half, one tablespoon at a time to thin as desired. Top with finely chopped pecans or walnuts, optional.
• Pour the frosting over the warm cake and spread evenly to the edges. Top with finely chopped nuts, if desired.