Preheat the oven to 400°F. Line two large baking sheets with parchment paper.
Toss together the apples, lemon juice, sugar, flour, cinnamon, and salt in a large bowl to combine.
Place one sheet of puff pastry on a lightly floured work surface and roll out to a 12-inch square. Cut into 4 smaller squares. Distribute some of the apple mixture in the center of each square of dough and drizzle about 1 tablespoon of caramel sauce over each pile of apples. Fold the pastry over the fruit to form a triangle and seal the edges with the tines of a fork. Brush the tops with the egg wash and cut a few slits in the top of each turnover. Place on the prepared baking sheets. Repeat with the remaining puff pastry, apple filling, and caramel sauce. Sprinkle each turnover with fleur de sel.
Bake for 20 to 22 minutes, until golden brown all over. Remove from the oven and let cool slightly before serving.