Preheat oven to 375°F (190°C). Line a cookie sheet with parchment paper and set aside.
Mix together apple slices, sugar, flour, almonds (if using) and raisins (if using) in a large bowl.
On a floured surface, roll out the thawed puff pastry dough with a rolling pin into a rectangular shape, about 12x16 inches.
Put the apple mixture down the bottom half of the long side of the pastry, leaving a 1-inch border around the outside.
Tuck in the short sides of the dough and then roll it up jelly-roll style.
Transfer strudel to the prepared baking sheet making sure to place seam side down.
Mix egg and water together and brush over strudel. Cut ¼-inch deep slashes diagonally across the top.
Bake for 35 to 40 minutes or until golden brown.
Let it cool before dusting with powdered sugar, and serve.