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 the mixture reaches a smooth consistency.
03 - In a separate bowl, sift together all-purpose flour, granulated sugar, brown sugar, cocoa powder, baking powder, baking soda, and salt.
04 - Add the dry ingredient mixture to the wet ingredient mixture. Stir gently until just combined, taking care not to overmix the batter.
05 - Fold the chocolate chips into the batter using a spatula or wooden spoon.
06 - Divide the batter evenly among the muffin cups, filling each approximately two-thirds 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 emerges with a few moist crumbs attached.
08 - Allow muffins to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.