Preheat oven to 350 degrees F.
Prepare a 9x5 inch loaf pan with oil and parchment paper.
In the bowl of a standing mixer, cream together butter, oil, and brown sugar. Add vanilla, egg, and mashed bananas. Mix until well combined.
In a separate bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
Add the flour mixture to the wet ingredients and mix just until combined. Do not over mix. Add semisweet chocolate chips to the batter and lightly stir.
Pour batter into a prepared 9x5 inch loaf pan. Tap and shake to release any air bubbles and smooth out batter.
Top with remaining bittersweet chocolate chips.
Bake at 350 degrees F for 50 minutes to an hour or until a toothpick inserted in the center comes out somewhat clean. Start checking on it at 50 minutes. It most often needs the full hour. Make sure you are not sticking the toothpick directly into a chocolate chip. That will deceive you into thinking it isn’t done yet. Do not overbake!
Allow to cool for 20 – 30 minutes and enjoy!