01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or lightly grease the cups.
02 - In a large mixing bowl, whisk together mashed bananas, eggs, vegetable oil, milk, and vanilla extract until smooth and well combined.
03 - In a separate bowl, sift together all-purpose flour, granulated sugar, brown sugar, unsweetened cocoa powder, baking powder, baking soda, and salt.
04 - Pour dry ingredients into the wet ingredient mixture. Stir gently with a spatula until just combined, being careful not to overmix the batter.
05 - Fold chocolate chips into the batter using a gentle folding motion to distribute evenly throughout.
06 - Divide batter evenly among the 12 muffin cups, filling each approximately three-quarters full. Top with additional chocolate chips if desired.
07 - Bake for 18 to 22 minutes, or until a toothpick inserted into the center of a muffin comes out with a few moist crumbs remaining.
08 - Allow muffins to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before serving.