Break the dark chocolate into pieces and melt in a bowl with the butter over a saucepan of water until melted and combined. Remove the bowl from the heat and set aside to cool for 10 minutes.

Put the egg, brown sugar and vanilla in a bowl and mix before beating in the melted chocolate mixture. Add the flour, baking powder and chocolate chunks, mixing well. Cover and chill for 1 hour until firm.

When ready to cook, preheat the oven to 180C/ Gas 4). Line 2 large baking trays with baking paper. Sift the icing sugar into a small bowl.

Using an ice cream scoop or a rounded dessert spoon, take a scoop of the chocolate mixture and press the rounded side down in the icing sugar to give it a sugar crust.

Arrange the sugared scoops on the baking trays, leaving room to spread. Bake for 15 minutes until risen, cracked, and just firm – the centre should remain soft. Leave to cool on the trays. Delicious served warm or cold.