4. Place pastry on prepared baking sheet. Sprinkle walnut mixture along long edge, leaving a 1-inch (2.5 cm) border. Scrape apple mixture over top of walnut mixture. Starting with border closest to you, lift pastry up and over apple mixture, rolling to cover completely. Place seam side down on pan; pinch ends to seal and tuck under strudel.
5. Whisk egg with water; brush over top of strudel. With a small, sharp knife, cut 3 or 4 slits in the top of the strudel to allow steam to escape.
Tip: Serve strudel with vanilla ice cream on the side, if desired. Substitute walnuts with pecans or almonds.
6. Bake for 40 to 45 minutes or until pastry is golden brown.
1. Preheat oven to 375°F (190°C). Line baking sheet with parchment paper; set aside.