Preheat oven to 325°F. Lightly grease two bread pans and then set aside. In a large bowl, cream butter and sugar. Then mix in eggs. Next add the vanilla and sour cream. In a separate bowl whisk flour, cocoa powder, baking powder, baking soda and salt. Slowly add to sugar mixture and stir until combined. Fold in bananas and chocolate chips (reserve a few for the top). Top with with extra chocolate chips if desired. Pour into 2 large loaf pans or 4 small loaf pans. You can also make 24 muffins with this recipe.
Bake for 1 hour in a loaf pan, 35-45 minutes in a small loaf pan or 20-25 minutes in a muffin pan. Make sure it comes clean with a toothpick.
Once the bread is cooked, allow to cool in the pan for at least 10 minutes and then remove the bread and place on a cooling rack.