Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper, leaving an overhang to easily lift the brownies out later.

In a medium bowl, mash the overripe bananas until smooth. Set aside.

In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined. Whisk in the eggs one at a time, followed by the vanilla extract and mashed bananas.

Sift the all-purpose flour, cocoa powder, and salt into the wet ingredients. Gently fold with a spatula until just combined. Do not overmix. Fold in chocolate chips if using.

Pour the batter into the prepared baking pan and smooth the top. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out with moist crumbs.

Allow the brownies to cool completely in the pan on a wire rack.

While brownies cool, prepare the glaze. Whisk together powdered sugar, melted butter, vanilla, and 1 tablespoon of milk. Add more milk as needed to reach a thick, pourable consistency.

Pour the glaze over the completely cooled brownies. Let the glaze set for 15 minutes before lifting the brownies out of the pan and slicing into squares.