Start by peeling the apples, cut them in half, remove the core and finally, cut them into strips.
Transfer everything to a medium bowl, add the brown sugar, the cinnamon powder, the juice of half a lemon, mix and set aside.
Now, on the sheet of puff pastry, brush 2 tablespoons of strawberry jam right on the center of the pastry.
Place the apple strips on top of the jam, covering all of it.
Then, add the raisins, spreading well, the chopped-up walnuts, close it by covering the filling with one of the ends of the pastry sheet, pressing the edges well to seal it.
Brush the top of this pastry covering the filling with 2 more tablespoons of strawberry jam and cover the jam with the other end of the pastry sheet.
Then, using a spatula as a guide, make shallow cuts on the pastry, dividing it into 3 equal pieces.
Using the same spatula, make a few shallow cuts on top of each piece we had cut.
Brush a mixture of two egg yolks beaten with one tablespoon of milk over everything.
Add 6 slices of the apples we prepared earlier and finally, sprinkle everything with brown sugar to taste.
Take it to a preheated oven at 180° C (350° F) and bake for 35 minutes.
Serve.