1. Preheat oven to 400°F. Roll thawed puff pastry sheet out to a rectangle.
2. Use a pizza cutter or sharp knife to cut 8 equal rectangles. Spoon 1-2 Tablespoons Nutella on the bottom half of each rectangle, leaving a 1/2 inch of space.
3. Add small amount of water to beaten egg white. Coat outside 1/2 of each rectangle with egg wash and use fork to press down and create a seal.
4. Apply egg wash to top of each sealed rectangle. Bake 15-20 minutes until golden brown. Allow to cool slightly and dust with powdered sugar if desired.