Instructions

• Preheat oven to 350°F. Line an 8x8-inch pan with parchment paper or foil and lightly spray the liner with non-stick cooking spray.
• In a large bowl, whisk together ½ cup melted unsalted butter, ¾ cup packed brown sugar, 1 room temperature egg, and 1 teaspoon vanilla until smooth.
• Add 1 cup all-purpose flour, ½ teaspoon baking powder, and ¼ teaspoon salt to the bowl and stir until just incorporated.
• Fold in ½ cup mashed banana (about 1 medium banana) and 1 cup chopped walnuts until evenly combined.
• Pour the batter into the prepared pan and spread it into an even layer. Bake for 20–25 minutes, or until the top is lightly brown and a toothpick inserted in the center comes out clean or with a few moist crumbs.
• Remove the pan from the oven and let the bars cool in the pan until completely cool to the touch (cooling to room temperature is best) before glazing.
• To make the brown butter glaze, melt ¼ cup unsalted butter in a medium saucepan over medium heat. Continue to cook, whisking or swirling, until the butter turns golden brown and gives off a nutty aroma. Remove from heat immediately to avoid burning.
• Whisk ¾ cup powdered sugar into the browned butter until the mixture is smooth and evenly combined.
• Pour the glaze over the cooled bars and spread evenly with a spatula. Allow the glaze to set before cutting into bars and serving.