Preheat the oven to 350°F. Line a 9-inch loaf pan with parchment paper leaving an overhang on the two longer sides. Grease the parchment paper with cooking spray.
In a large bowl, whisk together the flour, cocoa powder, sugar, baking powder, baking soda and salt.
In a separate medium bowl, whisk together the mashed bananas, eggs, vanilla extract, vegetable oil and sour cream.
Add the banana mixture to the dry ingredients and stir just until combined then stir in the chocolate chips. Scrape the batter into the prepared loaf pan then sprinkle additional chocolate chips on top of the loaf.
Bake the bread for 50 to 60 minutes until a toothpick inserted comes out clean. Remove the bread from the oven and allow it to cool in the pan for 10 minutes before using the parchment paper overhangs to lift the loaf out of the pan and onto a rack to cool completely.
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