Instructions:
- Preheat oven to 350°F (175°C). Grease an 8x8 inch (20x20 cm) metal baking pan and line it with parchment paper, ensuring an overhang on two sides for easy lifting.
- Place ripe bananas in a medium bowl and mash until smooth; ensure there are virtually no large chunks remaining.
- Whisk the melted butter into the mashed bananas until just combined. Whisk in the sugar, then incorporate the eggs one at a time, followed by the vanilla extract.
- In a separate, smaller bowl, whisk together the flour, cocoa powder, baking powder, and salt until uniformly mixed.
- Gently fold the dry ingredients into the wet ingredients using a rubber spatula. Stop mixing as soon as you see no more streaks of dry flour; do not overmix.
- Gently fold in the chocolate chips, if using.
- Pour the batter into the prepared pan and spread evenly. Bake for 28 to 32 minutes.
- Check for doneness: A toothpick inserted near the centre should come out with moist, sticky crumbs clinging to it, not wet batter.
- Allow the brownies to cool completely (at least 1 hour) on a wire rack in the pan before lifting out by the parchment overhang and slicing into squares.