Preheat oven to 350°F (175°C). Grease an 8-inch (20 cm) square baking pan and set aside.
In a large bowl, whisk together the melted butter and both sugars until smooth. Add the vanilla and eggs and mix until combined.
In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Slowly add the dry ingredients to the wet ingredients and mix until just combined.
Fold in the chocolate chips and mashed banana until evenly distributed.
Pour the batter into the prepared pan and spread evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let cool before cutting.
Interesting Facts
Brownies originated in the United States in the late 19th century.
The banana adds moisture and sweetness to the brownies.
Semi-sweet chocolate chips add richness and flavor.