Preheat the oven to 200ºC and line a baking tray with non-stick parchment paper.

Roll out the puff pastry sheet and flatten out with a rolling pin. Cut the pastry into 6 squares and spread with about 2 tablespoons of Nutella on each square leaving a border around the edges. Sprinkle with some hazelnuts.

Brush the edges with the beaten egg and fold the pastry in half. Use a fork to seal the edges of the puff pastry. Brush the outside of the pastry with more beaten egg and sprinkle with the demerara sugar and some more hazelnuts. Use a sharp knife to make 3 small cuts in the top of the pastry.

Bake in the preheated oven for about 15-20 minutes until the pastry has puffed up and is golden and flaky. Leave to cool for a few minutes before serving.

Be careful, the Nutella will be very hot!