Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking pan with butter or line it with parchment paper.

Mash 2-3 ripe bananas in a mixing bowl until smooth. Mix in melted butter, then add sugar, eggs, and vanilla, stirring until combined.

In a separate bowl, whisk together flour, baking soda, salt, and cocoa powder until no lumps remain.

Gradually add the dry mixture to the wet ingredients, mixing gently until just combined; do not overmix.

Stir in milk until smooth. If using, fold in chocolate chips.

Pour the batter into your prepared baking pan, spreading it evenly to the corners.

In a small bowl, combine brown sugar and cinnamon, then sprinkle this mixture over the brownie batter.

Bake for 25-30 minutes until edges pull away from the pan and a toothpick comes out clean.

Let the brownies cool in the pan for 10 minutes before transferring to a wire rack to cool completely, then slice into squares.