Line a baking sheet with parchment paper.

Cut the puff pastry sheet into 6 squares (at least 5x5 inches or 12x12 cm), you can also cut a small (about 1 inch or 2 cm thick) strip of pastry (the shorter side of the puff pastry sheet) to cut small "leaves" from it as a decoration (optional, see photos in the post).

Prepare the apples. While you're preparing the apples, your puff pastry should be in the fridge. Take it out only if you have everything else ready (all butter puff pastry can be very sticky and hard to work with and that's why must be very cold).

Peel the apples.

Using a small pairing knife and a teaspoon, core the apples but not all the way through (you should leave a small part of the core at the bottom of the apple to prevent the filling from falling out). See the photos in the body of the post for reference.

Fill the apple centers with chopped walnuts, then add a spoonful of chocolate hazelnut spread and sprinkle with some more nuts on top until the centers are full.

Place an apple on a one puff pastry square and sprinkle it with cinnamon.

Wrap each apple in a puff pastry square (take one square of puff pastry out of the fridge at a time). Make sure to pinch the edges of the pastry well at the top so that the pastry parcels don't split open but the apples don't have to be perfectly enclosed in the puff pastry, if you have some holes on the sides, this is fine. Place each wrapped apple on the parchment paper.

Optional: cut out small leaves out of the reserved stripe of puff pastry and place the leaves on top of each apple.

Make egg wash: beat the egg with a tablespoon of milk or water until combined. Brush your pastries with the egg wash.

Take the apples out of the oven. Let stand for 5 minutes to cool down slightly then dust with powdered sugar.

Serve with whipped cream on the side and enjoy!