Preheat oven to 350°F (175°C) and line a 12-cup muffin pan with cupcake liners.
In a medium bowl, whisk together flour, baking powder, baking soda, salt, and cinnamon.
In a large bowl, whisk melted butter, brown sugar, and granulated sugar until smooth.
Add mashed bananas, eggs, and vanilla extract; mix until fully combined.
Stir in milk.
Gradually fold in dry ingredients until just combined—do not overmix.
Gently fold in chocolate chips.
Divide batter evenly among cupcake liners (about ¾ full).
Bake for 18–20 minutes, or until a toothpick inserted comes out clean or with a few moist crumbs.
Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.