Cream butter, sugar, and vanilla together until pale in color. In a separate bowl, whisk together bananas, and eggs. Add the banana mixture to the creamed butter and mix until just combined. Preheat oven to 350°F.
Whisk together flour, cocoa powder, baking soda, and sea salt. Fold into wet ingredients.
Add sour cream and fold the batter again until just combined then fold in chocolate chips.
Grease loaf pans with butter or baking spray, optionally, line them with parchment paper. Divide batter evenly between the two prepared pans.
Bake for 35-45 minutes or until a toothpick inserted in the center comes out clean. Allow banana bread to rest for 10 minutes before removing from pan.