01 - Preheat oven to 350°F and line a 12-cup muffin tin with paper liners or grease lightly.
02 - In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt until evenly mixed.
03 - In a separate bowl, whisk mashed bananas, sugar, oil (or melted butter), eggs, vanilla extract, and milk until smooth.
04 - Pour wet mixture into dry ingredients and stir gently until just combined without overmixing.
05 - Fold semisweet chocolate chips carefully into the batter.
06 - Divide batter evenly among muffin cups, filling about three-quarters full. Optionally top with extra chocolate chips.
07 - Bake for 18 to 22 minutes or until a toothpick inserted into a muffin center comes out with a few moist crumbs.
08 - Let muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.