Put the chocolate, butter and sugar together in a large, microwave safe bowl.
Microwave the bowl in 30 second bursts, stirring between bursts until the butter and chocolate has melted.
Add the mashed bananas. Whisk well. This also helps to cool the mixture down a little.
Whisk in the eggs.
Add the flour and baking powder. Fold through.
Line a muffin tray with muffin cases and spoon the mixture in evenly.
Bake for approximately 20 minutes until well risen and a rich chocolate brown.
Allow to cool on a wire rack before serving.
Store these muffins in an airtight container to keep them fresher for longer. Allow the muffins to cool completely before sealing them in the container and placing somewhere dark, dry and cool such as a kitchen cupboard or pantry. They should keep for up to a week.