Preheat your oven to 350°F (175°C) and line an 8x8-inch baking dish with parchment paper.
In a large mixing bowl, mash the banana with a fork, ensuring you have exactly ½ cup.
Add the nut butter (we used peanut butter), maple syrup, egg, and vanilla extract to the bowl. Whisk until the mixture is smooth and well combined.
Stir in the cocoa powder, and baking soda. Mix until fully incorporated, then fold in the 1/2 cup of the chocolate chips.
Pour the batter evenly into the prepared baking dish and sprinkle the remaining chocolate chips on top.
Bake for 27-28 minutes, or until a knife inserted into the center comes out with a few moist crumbs. Avoid over-baking for the best texture.
Allow the brownies to cool in the pan on a wire rack for at least 30 minutes (or, ideally, until completely cooled) before slicing.