Beat in the egg and mashed banana until well combined.

Add the flour and the baking powder and mix well – you should now have a sticky, light dough.

Fold in the dark chocolate chunks, keeping a large handful (about 50g) back to go on top later.

Use a large ice cream scoop the dough, flattening off against the side of the bowl, then roll the dough into a ball with your hands. This is the best way to get 20 equally sized cookies. If you find the dough sticky, try using wet hands to shape the dough.

Place the balls of dough on baking sheets lined with greaseproof paper, being sure to place each cookie at least an inch apart so that they don’t stick together when they spread.

Bake for 8-10 minutes until golden at the edges. Get them out of the oven before they’re fully browned so that they stay chewy when cool.

While still hot, scatter the remaining chocolate chunks on top.

Allow to cool on the tray until firm enough to transfer to a wire rack to cool completely.