Preheat your oven to 180°C (350°F) and line a muffin tin with paper liners or lightly grease it.
Peel the overripe bananas and mash them thoroughly in a large bowl until smooth and fragrant, with streaks of brown spots showing.
Add the oil or melted butter to the mashed bananas, then sprinkle in the brown sugar. Mix everything together until the mixture is glossy and well combined, with a gentle aroma of caramelized banana.
In a separate bowl, sift together the flour, cocoa powder, baking powder, and a pinch of salt. Whisk to combine evenly.
Pour the dry mixture into the banana mixture. Gently fold with a spatula until just combined — the batter should be thick, with some streaks of flour still visible, but no dry patches.
Crack the eggs into the batter and fold carefully until the mixture is smooth and slightly glossy, ensuring the batter is well incorporated but not overmixed.
Fold in the chocolate chips evenly, distributing them throughout the batter. The mixture should be thick but scoopable.
Scoop the batter into the prepared muffin tin, filling each cup about three-quarters full and gently tapping the tray to settle the batter.
Bake in the preheated oven for 20-25 minutes, until the muffins are risen, cracked on top, and smell rich with chocolate and banana aroma. Check doneness by inserting a toothpick into the center; it should come out with moist crumbs.
Allow the muffins to cool in the tin for about 5 minutes, then transfer them to a wire rack to cool completely. The tops should be crackled and slightly shiny, inviting you to take a bite.
Serve these muffins warm or at room temperature, perhaps with a sprinkle of sea salt or a drizzle of extra chocolate for an indulgent touch. Enjoy the soft, moist crumb with bursts of chocolate and the deep caramel flavor of bananas.
