Line 2 baking trays with baking parchment. In a mixing bowl, beat together the butter and sugar until creamy and well blended. Beat in the egg yolk and Vanilla Paste.

Sift the flour and Baking Powder on top and add the Chocolate Chunks. Mix together to form a firmish dough. Split the dough into 8 equal pieces and roll in a ball. 

Put the chocolate hazelnut spread in a small uncut piping bag and snip off about 1cm (1/2inch) from the end. Working on one cookie dough ball at a time, push your thumb into the centre to make a deep hollow, and then pipe a small blob of chocolate spread into the hollow. Carefully mould the dough over the filling, making sure it is well sealed, and then gently roll back into a ball. 

Arrange the filled cookie dough balls on the prepared baking trays spaced a little apart, then chill for about 30 minutes until firm.

Ten minutes before baking, preheat the oven to 190˚C (170˚C fan oven, 375˚F, gas 5). Bake the cookies for 12 - 15 minutes until lightly golden. Cool on the trays for 5 minutes before transferring to a wire rack. These cookies are best served warm to enjoy the melting middle!