Preheat oven to 350 degrees. Spray non-stick cooking spray on an 8x8 square pan. Place a piece of parchment paper on the bottom and spray with non-stick cooking spray.
In a large mixing bowl, add in the melted butter, granulated and brown sugar, and mashed banana. Mix until incorporated.
Add in eggs, vanilla extract, banana, extract, and liqueur and mix for 2 minutes until thick and fluffy.
Add in the cocoa powder and flour and stir until combined.
Spread into the prepared 8x8 inch square pan. Place in the oven and bake for 30-35 minutes or until done. Place a toothpick in the center of the brownies and if it comes out clean or with moist crumbs, it's done. If it still have batter on it, let it go a few more minutes before testing it again.