Keep 2 tablespoonfuls of chopped hazelnuts aside in a small bowl.
Place the rest of the chopped hazelnuts in your food processor and blitz until smooth. Add the cacao powder, maple syrup, vanilla extract and sea salt.
Melt the chocolate in a small bowl set over a larger bowl of boiling water.
Roll the hazelnut mixture into 12-14 bite-size balls and pop a whole hazelnut in the centre of each ball.
Dip in the melted chocolate and sprinkle with the chopped hazelnuts.
Place in the fridge for half an hour before serving.