Combine egg, nutella and flour and mix well. Add chocolate and then form dough into 12 balls.

Place in fridge until firm (or ideally over night) - this helps to intensify the flavours and prevents cookies from spreading). Meanwhile preheat oven to 175C and line a baking tray with baking paper. Place balls of dough on tray and leave as balls (i.e. do not press them down).

Bake cookies for 15 minutes. Be careful not to over bake (they continue cooking slightly on the tray once out of the oven).