Begin by melting the unsalted butter in a small saucepan over medium heat. Stir constantly for about 5-7 minutes until the butter turns a beautiful golden brown and emits a nutty aroma. Once browned, remove the pan from the heat and allow the butter to cool slightly while preparing the other ingredients.

In a large mixing bowl, pour the cooled brown butter and mix in the granulated sugar until well combined. Add in the large egg and teaspoon of vanilla extract, stirring until the mixture is smooth. Then, gently fold in the three mashed bananas until everything is well integrated.

In a separate bowl, whisk together the all-purpose flour, baking soda, baking powder, salt, and ground cinnamon. Once mixed, gradually incorporate the dry ingredients into the wet banana mixture, stirring gently just until combined.

Carefully fold in the brown sugar, ensuring even distribution throughout the batter.

Preheat your oven to 350°F (175°C) while you prepare your loaf pan. Grease a 9x5-inch loaf pan generously.

Pour the prepared batter into the greased loaf pan, using a spatula to smooth the top for an even rise. Optionally, top the batter with dollops of sugar cookie dough.

Place the loaf pan in the preheated oven and bake for 50-60 minutes. It's done when a toothpick inserted comes out clean.

Once baked, remove the loaf from the oven and allow it to cool in the pan for about 10 minutes. Transfer the banana bread to a wire rack to cool completely.