Preheat your oven to 350°F (175°C) and prepare a 9x13-inch baking pan by greasing or lining it with parchment paper.

Mash ripe bananas in a mixing bowl, then add melted butter, granulated sugar, eggs, and vanilla extract. Mix until creamy.

In a separate bowl, whisk together flour, baking soda, salt, and cocoa powder, then fold into the wet mixture carefully.

Gently fold in the milk and optional chocolate chips into the batter until just combined.

Pour the batter into the baking pan and spread it evenly across the surface.

In a small bowl, combine brown sugar and ground cinnamon, sprinkle over the batter, then dot with butter pieces.

Bake in the preheated oven for 25-30 minutes. Check doneness with a toothpick; it should come out with moist crumbs.

Allow the brownies to cool in the pan for 10 minutes, then move them to a wire rack to cool completely before slicing.