Preheat the oven to 350°F (175°C) and line a standard 12-cup muffin tin with paper liners.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.

In a large mixing bowl, add the mashed bananas (or, if mashing directly into the bowl, measure out 360g of banana flesh for accuracy). Add both the granulated and coconut (or brown) sugar, then whisk until the mixture looks glossy and syrupy. Whisk in the eggs, cooled melted butter, and vanilla extract until well blended. Add the dry ingredients to the wet and gently fold them in using a spatula or spoon until just combined—be careful not to overmix.

To make the fudge swirl, place the chopped bittersweet chocolate and cream in a small microwave-safe bowl. Microwave until the cream is hot, then stir until the chocolate melts and the mixture becomes smooth. Stir in ¼ cup of the banana batter and mix vigorously until fully incorporated and thickened—it may look separated at first, but keep stirring until smooth and cohesive.

Evenly divide the muffin batter among the prepared liners. Drop about 1 teaspoon of the fudge mixture into the center of each muffin, then swirl it through using the blunt side of a knife, gently folding the batter over to distribute the fudge throughout. Press a few dark chocolate chunks into the top of each muffin if desired.

Bake for 18 to 20 minutes, or until the tops are set and a toothpick inserted into the center comes out with moist crumbs. Cool the muffins on a wire rack—they’re absolutely delicious while still warm!