Cut the pastry sheet in two, and cut strips into one side of each. Add the chocolate spread in the middle, sprinkle with hazelnuts and close the pastry, forming a "braid" on the top. Repeat for the other half of the pastry sheet.
Brush the pastries with the egg yolk and place them in a baking dish lined with parchment paper. Bake in a preheated oven at 180° C for 15' – 20' until golden brown. Leave to cool and serve.