Preheat your oven to 180°C (350°F) and line your muffin tin with paper liners or grease it well. Gather all your ingredients so they're ready to go.
Peel and mash the overripe bananas with a fork or potato masher until mostly smooth, leaving a few small lumps for texture. This releases their fragrant, sweet aroma and makes mixing easier.
In a large mixing bowl, whisk together the flour, brown sugar, and baking powder until evenly combined. This creates a fluffy, even dry mixture for the batter.
In a separate bowl, melt the butter or coconut oil, then whisk in the eggs and vanilla extract until the mixture is smooth and slightly frothy. This forms the wet base for your batter.
Pour the wet mixture into the mashed bananas and stir gently with a spatula or spoon until just combined. The batter should be moist and slightly sticky.
Gradually fold the wet ingredients into the dry mixture, mixing gently until everything is just combined. Be careful not to overmix—small lumps are okay.
Fold in the chilled dark chocolate chunks evenly through the batter, distributing pockets of melted chocolate for those delightful surprises in each bite.
Divide the batter evenly among the muffin cups, filling each about three-quarters full. Tap the muffin tin gently on the counter to settle the batter and release air bubbles.
Bake in the preheated oven for 20-25 minutes, or until the tops are golden and a toothpick inserted into the center comes out clean with moist crumbs.
Remove the muffins from the oven and let them cool in the tin for about 5 minutes. Then transfer them to a wire rack to cool completely, allowing the chocolate to set just enough for easy handling.
Enjoy these muffins warm or at room temperature—perfect for a quick breakfast or a cozy snack with a glass of milk or a cup of coffee. Store leftovers in an airtight container for up to 2 days, or freeze for longer keeping.
