Preheat your oven to 180°C (350°F) and line a muffin tin with paper liners or grease it well.
Peel the overripe bananas and mash them thoroughly with a fork or potato masher until they’re almost liquefied—this releases their natural sweetness and makes a sticky, fragrant base.
In a small bowl, melt the butter gently—about 20 seconds in the microwave—then let it cool slightly before adding it to the mashed bananas.
Pour the melted butter into the mashed bananas, then crack in an egg and whisk everything together until the mixture is smooth and fragrant, about 30 seconds.
In a separate large bowl, whisk together the flour, brown sugar, and baking powder until evenly combined.
Gently fold the dry ingredients into the banana mixture with a spatula or spoon, just until no streaks of flour remain—be careful not to overmix, as this keeps the muffins tender.
Roughly chop the dark chocolate and fold it into the batter, ensuring an even distribution of melty pockets throughout.
Spoon the batter into the prepared muffin tin, filling each cup about three-quarters full to allow room for rising.
Bake for 20-25 minutes, or until the muffin tops are golden and cracked slightly, and a toothpick inserted into the center comes out with moist crumbs.
Remove the muffins from the oven and let them cool in the tin for about 10 minutes—this helps set their crumb and makes them easier to handle.
Transfer the muffins to a wire rack and cool completely before serving. Enjoy warm or at room temperature, perhaps with a drizzle of melted chocolate or a dusting of cocoa powder for extra indulgence.
