Method

Blitz the hazelnuts in a food processor until finely chopped and place to one side on a plate.
Line two large baking sheets with grease proof paper.
In a large mixing bowl cream together the butter and sugar with the vanilla paste until light and fluffy. Beat in the egg and with a splash of milk. Gradually stir in the flour and 25g of the blitzed hazelnuts and the chopped chocolate.
Mix into a firm dough and shape into 2 x 10cm logs. Wrap in clingfilm and leave to firm up in the fridge for an hour or so. When you’re ready to bake pre heat the oven to 160c/gas mark 3. Remove the log from the fridge, unwrap and roll in the plate of chopped hazelnuts. Slice in the log into rounds and place on the baking sheet. Bake the cookies in the oven for 20 minutes until golden brown. Allow to cool for a few minutes on the tray and transfer to a cooling rack.
When you’re ready to serve the chocolate mousse, remove from the fridge and sieve over a little cocoa powder and serve with the cookies.