Preheat the oven to 400°F (200°C). Line 2 baking sheets with parchment paper. Whisk the egg with a fork and set aside.
Place a sheet of puff pastry on a baking paper. Spread Nutella evenly over the surface, reaching the edges. Line the second puff pastry sheet on top and gently press the two together.
Using a sharp knife or pizza cutter, slice the pastry into 1-inch (2.5 cm) strips. Hold each strip at both ends and twist gently a few times.
Place the twists on your prepared baking sheets, spacing them about 1.5 inches (3.5–4 cm) apart. Press the ends down slightly to keep them from unraveling.
Brush the twists with the beaten egg, sprinkle with brown sugar, and bake for 15-20 minutes or until the twists have puffed and are golden brown.
Cool slightly and enjoy warm—or let them cool completely and serve with coffee or milk.
Notes
Don't overfill with Nutella. It spreads as it bakes, so a thin, even layer is enough.
Thaw the puff pastry fully, as cold pastry cracks and warm pastry becomes sticky. Aim for just-right.
Try flavor twists with chopped hazelnuts or a sprinkle of cinnamon with the brown sugar.