Preheat oven to 350°F (175°C). Grease or line an 8×8-inch (20×20 cm) baking pan.
Mash the bananas in a bowl until smooth.
Mix wet ingredients: Stir in melted butter, sugar, vanilla, and egg until well combined.
Sift in dry ingredients: Add cocoa powder, flour, baking powder, and salt. Mix until just combined.
Fold in chocolate chips for extra richness.
