Preheat the oven to 190°C (375°F). Line a baking sheet with parchment paper.

In a bowl, mix the apples, sugar, cinnamon, lemon juice, and optional raisins or nuts. Set aside.

Roll out the puff pastry on a floured surface to a rectangular shape. Place the apple mixture in the center, leaving a 1-inch border around the edges.

Fold the sides of the pastry over the filling, then roll it up tightly. Seal the edges with a little water and place the strudel seam-side down on the baking sheet.

Brush the top with melted butter and make a few slits on the surface to allow steam to escape.

Bake for 25-30 minutes, or until golden brown and crisp. Let cool slightly.

Dust with powdered sugar before serving.