Preheat the oven to 400 degrees F. Mix the granulated sugar, corn starch, apple pie spice and salt in a shallow dish.
Cut both pieces of puff pastry in half so you have 4 rectangles. Use a rolling pin to gently roll out any cracks or creases. Then lay them on a large parchment paper lined baking sheet.
Roll 4 peeled and cored apples in the sugar mixture and set one in the middle of each piece of puff pastry. Unwrap the caramels and stick 3 caramel squares down in the center of each apple.
To wrap each apple, pull the short sides of the puff pastry halfway up the side on the apple and hold them there with one hand. Then lift the longer sides up to the top and pinch the seams together on each side (over the short edges) to completely cover the apple. Pinch the excess puff pastry together at the top to seal, then arrange the flaps in a pretty way.
Then whisk 2 eggs with 2 tablespoons of water and brush the egg wash over each apple. Sprinkle the tops with Demerara sugar.
THIS IS THE MOST IMPORTANT STEP... Place the baking sheet with the wrapped apples in the freezer for 15-20 minutes to harden the puff pastry. This will ensure your puff pastry bakes in place and does not sag to the bottom. But don't leave them in the freezer longterm. You don't want the apples to freeze.
Once the puff pastry is hard, place the baking sheet in the oven and bake for 25 minutes, until puffy and golden. Cool for 10 minutes before serving. Drizzle the tops with extra caramel sauce if you like!