Preheat the oven to 350 degrees F.
Place the hazelnuts on a baking sheet in a single layer. Toast the hazelnuts in the oven until lightly golden brown, about 10 minutes.
Increase the temperature to 400 degrees F and line a couple of baking sheets with parchment paper; set aside.
Add the hazelnuts and sugar to a food processor and pulse until the hazelnuts are finely ground but not pureed.
Take a sheet of puff pastry and place in on a lightly floured surface. Using a rolling pin, roll out the puff pastry so it's about 1/2 inch bigger on all 4 sides. Brush the surface of the pastry with some egg wash and sprinkle half of the nut-sugar mixture evenly over the top. Sprinkle over half of the grated chocolate and, using your hands, press down gently so the topping can adhere to the pastry a bit better. Cut the sheet of pastry into 3/4-inch slices using a sharp knife or a pizza cutter. Give each strip 2 or 3 twists and place them on your prepared baking sheets. Brush them carefully with some more egg wash and pop them in the freezer for 15 minutes. Repeat with the remaining pastry and topping ingredients.
Bake the twists until lightly golden brown, about 20 minutes. Allow them to cool for about 10 minutes before serving.
Mix it up! Use sweet or savory fillings. For a savory idea, try grated Parmigiano-Reggiano plus chopped thyme or oregano, or Asiago cheese with a pinch of cayenne--so good!!