01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or lightly grease with cooking spray.
02 - In a large mixing bowl, whisk together mashed bananas, eggs, vegetable oil, milk, and vanilla extract until thoroughly combined and smooth.
03 - In a separate medium bowl, sift together all-purpose flour, granulated sugar, brown sugar, cocoa powder, baking powder, baking soda, and salt.
04 - Pour dry ingredients into wet ingredients. Fold gently with a spatula until just combined—some small lumps are acceptable. Do not overmix.
05 - Fold chocolate chips into batter until evenly distributed.
06 - Divide batter evenly among 12 muffin cups, filling each about three-quarters full. Top with additional chocolate chips if desired.
07 - Bake for 18 to 22 minutes until a toothpick inserted into the center comes out with a few moist crumbs.
08 - Let muffins cool in pan for 5 minutes, then transfer to a wire rack to cool completely.