Preheat oven to 350°F.
In the bowl of a stand mixer, add the butter, sugar and corn syrup and mix until smooth.
Stir in the vanilla, eggs, mashed bananas and sour cream.
Add the baking soda, salt and flour and stir just until combined.
Scoop 1 cup of the batter into a separate bowl and add the cocoa powder. Stir until combined.
To the remaining batter (with no cocoa powder), add the ½ cup of mini chocolate chips. Stir.
Scoop half of the batter into the bottom of a parchment-lined loaf pan.
Then, scoop the chocolate mixture on top and spread carefully.
Lastly, scoop the remaining batter on top and spread out evenly.
Sprinkle the 2 tablespoon mini chocolate chips on top and bake for 55-60 minutes.