Preheat your oven to 350°F (175°C) and grease an 8×8-inch baking pan or line with parchment paper.

In a large mixing bowl, mash ripe bananas using a fork or potato masher until mostly smooth with a few lumps.

Add melted butter, granulated sugar, eggs, and vanilla extract to the mashed bananas and stir until fully combined.

In a separate bowl, whisk together flour, baking soda, salt, and cocoa powder. Gradually add dry ingredients to the wet mixture, stirring gently.

Fold in chocolate chips evenly into the batter.

For an optional crumb topping, mix flour, brown sugar, and melted butter until crumbly and sprinkle over the batter.

Pour the brownie batter into the prepared baking pan and smooth the top.

Bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out with moist crumbs.

Allow the brownies to cool for at least 10 minutes before slicing into squares.