Instructions

• Preheat oven to 350°F (175°C). Line a 9x9-inch baking pan with aluminum foil and spray the foil with cooking spray; set the pan aside.
• In a large bowl, whisk together 1 large egg, 1/2 cup packed light brown sugar, 1/4 cup liquid-state coconut oil (or substitute), 1/4 cup sour cream (or Greek yogurt), and 2 teaspoons vanilla extract until combined.
• Add 1 cup mashed ripe bananas (about 2 large or 3 medium bananas) to the bowl and stir to incorporate.
• Add 1 cup all-purpose flour, 1/2 teaspoon baking powder, 1/2 teaspoon baking soda, and a pinch of salt (optional). Fold with a spatula or stir gently just until the dry ingredients are incorporated; do not overmix.
• Turn the batter into the prepared pan, smoothing the top lightly and pushing into the corners and sides as needed.
• Bake for about 27 to 28 minutes, beginning to check at 25 minutes. The bars are done when the center is golden and set, springs back lightly when touched, and a toothpick inserted in the center comes out clean or with a few moist crumbs but no wet batter.
• Remove the pan from the oven and set it on a wire rack to cool while you make the glaze. The bars may be glazed while still slightly warm.
• To brown the butter: place 6 tablespoons unsalted butter in a small saucepan over medium‑high heat. Cook, stirring or swirling the pan and watching closely, until the butter turns amber to brown and smells nutty, about 5 minutes depending on pan size. Transfer the browned butter, including the brown bits, immediately to a large mixing bowl to stop the cooking.
• Add 2 cups confectioners’ sugar, 2 teaspoons vanilla bean paste (or the seeds from 1 large vanilla bean; if substituting vanilla extract, use 1 tablespoon), and a pinch of salt (optional) to the bowl with the browned butter.
• Slowly add about 1/4 to 1/3 cup cream or milk while whisking, until the mixture is smooth. If necessary, add additional cream (or more confectioners’ sugar) to reach a medium-thick, easily pourable glaze.
• Evenly pour the glaze over the bars in the pan, smoothing lightly with a spatula if needed.
• Allow the bars to cool in the pan, uncovered, for at least 2 to 3 hours (or leave overnight and cover with a sheet of foil) before slicing and serving so the glaze can set.