Heat the oven to 375°F. Beat the egg and water in a small bowl with a fork or whisk. Stir the sugar, flour and cinnamon in a medium bowl. Add the apples and raisins and toss to coat.
Unfold the pastry sheet on a lightly floured surface. Roll the pastry sheet into a 16 x 12-inch rectangle. With the short side facing you, spoon the apple mixture onto the bottom half of the pastry sheet to within 1 inch of the edge. Roll up like a jelly roll. Place seam-side down onto a baking sheet. Tuck the ends under to seal. Brush the pastry with the egg mixture. Cut several slits in the top of the pastry.
Bake for 35 minutes or until the strudel is golden brown. Let the strudel cool on the baking sheet on a wire rack for 20 minutes. Sprinkle with the confectioners' sugar, if desired.
Ingredient Note: For some nutty crunch, 1/4 cup sliced almonds may be added with the apples and raisins.
Recipe Note: The strudel may be served with Vanilla Sauce: Stir 3/4 cup milk, 1/2 cup light cream, 1/3 cup sugar, 4 egg yolks, beaten and 1/2 vanilla bean in a 2-quart saucepan. Cook and stir over medium heat until the mixture boils and thickens. Remove the saucepan from the heat. Cover and refrigerate for at least 1 hour. Remove the vanilla bean. Makes about 1 3/4 cups.