In a large bowl, whisk together the butter, banana, sugar, oil, sour cream, buttermilk, egg, espresso, baking powder, baking soda, and salt until combined. Add the flour and gently mix until almost combined. Fold in the diced bananas, chocolate chips, and cacao nibs if using. Be careful not to overmix the batter. It should not be completely smooth; there should be some visible lumps and bumps.