• Preheat oven to 350°F. Grease a 15X10 jellyroll baking pan (see recipe notes for 9x13 pan).
• In a large bowl, cream together the softened butter, sugar, and brown sugar until light and fluffy, about 3-5 minutes. Beat in the eggs, mashed bananas and vanilla until well combined.
  ½ cup unsalted butter, 1 cup granulated sugar, ½ cup packed brown sugar, 3 large eggs, 1 ½ cups mashed ripe bananas, 1 teaspoon vanilla extract
• Add in flour, baking soda and salt. Mix well into the mixture.
  2 cups gluten free all-purpose flour, 1 teaspoon baking soda, ¼ teaspoon salt
• Pour the batter into prepared baking pan and smooth evenly. Bake for 20-25 minutes, rotating pan halfway through baking. The bars are done when toothpick inserted in middle comes out clean. Meanwhile, start the frosting.

Brown Butter Frosting

• As soon as bars come out of oven, or a little before, begin the frosting. In a medium saucepan melt the butter. Once the butter is fully melted watch carefully and stir occasionally so butter doesn't burn. First the butter will foam, then the milk solids will start to settle at the bottom. Watch for the milk solids to turn from white to golden brown. Once that happens, immediately remove from heat.
  ½ cup unsalted butter, 2 ½ cups powdered sugar, ¼ teaspoon salt, 3 tablespoons milk
• Whisk in 1 cup powdered sugar, salt, and milk. Stir in the remaining powdered sugar. Add more milk if necessary for a thinner consistency. Immediately pour and gently spread on warm bars using an offset spatula. Cool slightly before slicing and serving.