Preheat the oven to 400˚F. Line a large baking sheet with parchment paper and set aside.
Preheat a large skillet over medium heat. Add 2 tbsp butter and 3 peeled, cored, and sliced apples. Cook for a few minutes, until softened, then add 1 tsp cinnamon and ¼ cup brown sugar. Continue cooking for anther 5-7 minutes or until they are soft and caramelized. Take the skillet off the heat and set aside to cool off.
Place thawed puff pastry dough on a counter top or a cutting board and cut the dough in half lengthwise.
Place one half on a baking sheet with parchment paper. Scoop the caramelized apple slices in the middle of the dough, leaving about 1 inch on the sides.
Whisk an egg in a bowl, and using a pastry brush, brush the edges on the puff pastry dough.
Top it with another layer of dough and seal the edges, by pinching them on the sides. Using a pairing knife, make a few cuts in the center, creating vents.
Brush the top with more egg wash and top with the raw or coarse sugar.
Bake at 400˚F for about 20 minutes or until the top is golden/brown.