Preheat the oven to 400˚F. Line a baking sheet with parchment paper or a silicone mat.
On a clean work surface that's been lightly floured, lightly roll out the puff pastry sheet. Cut in half lengthwise. Cut horizontally to create 6 squares.
Spread one half of each pastry square with 2 Tbsp Nutella. Leave a border around the edges so you can seal the pastry.
Sprinkle each dollop of Nutella with chopped hazelnuts.
Brush the edges of the entire square with egg.
Fold the pastry over the Nutella half. Use a fork to seal the edges.
Brush the tops with egg. Sprinkle with raw sugar.
Use a sharp knife to cut three slits in the top of each pastry.
Bake for 15 to 20 minutes until golden brown and puffed.
Cool for a few minutes on the pan before serving warm.