Preheat oven to 180˚C.

Melt the dark chocolate, butter and espresso together over low heat in a saucepan then take off the heat. 

Stir in the vanilla and beat in the egg and dark brown sugar.

Mix in the flour and baking powder then fold in your chocolate chips.

Take rounded tablespoonfuls of batter and drop onto a lined cookie sheet - you may need to use two trays as they need a couple of inches space to allow for some spreading on baking.

Bake for approximately 8 minutes by which time they will have puffed and spread a little. They will have a dry surface but a hint of wibble in the middle showing their centres are going to be nice and fudgy when cool.

Cool on the tray for 10-15 minutes before transferring to a rack to finish cooling.