Preheat oven to 375. Line two baking sheets with parchment paper or silicone baking mats. Set aside.
Evenly spread the Nutella on each puff pastry sheet. Sprinkle coarsely chopped hazelnuts over one sheet.
Place the puff pastry sheet without hazelnuts over the other sheet. The Nutella sides should now be facing each other.
Cut the layered sheet lengthwise into 1/2-inch-wide strips. Gently twist each strip several times and roll the twisted pastry into a coil. Place on the prepared baking sheet and tuck the end of the twist under the coil.
Brush each twist with butter and sprinkle with brown sugar.
Bake the twists for 20-25 minutes, or until lightly golden.