Preheat oven to 350°F. Grease or line a 9×5 loaf pan.
Mash the bananas until mostly smooth.
Mix in melted butter, brown sugar, granulated sugar, egg, and vanilla.
Add flour, cocoa powder, baking soda, and salt. Mix just until combined.
Fold in the chocolate chips.
Pour into your loaf pan and sprinkle extra chocolate chips over the top.
Bake for 50–60 minutes, until a toothpick inserted into the center comes out with a few moist crumbs (melted chocolate on it is fine!).
Let cool in the pan for about 15 minutes before removing.
