Preheat oven to 350 degrees. Spray a 9x5x3 loaf pan with non-stick spray.
Add the butter and sugars to a mixing bowl and mix until well combined.
Beat in the egg, vanilla, banana, and sour cream.
Stir in the flour, cocoa powder, and baking soda.
Pour mixture into prepared loaf pan.
Sprinkle the top with chocolate chips and gently press them into the batter.
Bake for 70 minutes or until a tester comes out clean. If you under bake this, the center will sink upon cooling.
Let bread cool completely before cutting and serving.
PLEASE NOTE: I baked this bread in a ceramic loaf pan. If you're using a glass or metal pan, your baking times may vary. Keep an eye on the bread and check with a tester before removing from the oven.