Preheat oven to 400 degree F. Lightly grease 2 cookie sheets; set aside. In a small bowl beat together egg and 1 tablespoon water; set aside.
Unfold one pastry sheet on a lightly floured surface. Roll to a 12-inch square. Cut into nine 4-inch squares. Spread the center of each square with about 1 tablespoon of the chocolate-hazelnut spread, leaving a 1-inch border around the edge. Divide half of the hazelnuts, dates, and chocolate pieces evenly among the prepared pastry squares, placing atop spread. Brush edges of squares with egg mixture. Fold each to form a triangle and crimp edges with a fork to seal.
Prick tops with the fork. Transfer to one of the prepared cookie sheets. Brush with egg mixture. Bake for 12 to 15 minutes or until golden. Repeat with remaining ingredients. Cool slightly on wire racks. Serve warm. Makes 18 puffs.