Mix the flour and salt in a large bowl. Add the ice cold butter and rub it into the flour using your fingers or a pastry cutter, leaving visible chunks of butter but incorporating it slightly.

Slowly pour in the ice cold water a little at a time, stirring with a fork and then working it with your fingers until the dough comes together.

Place the dough on a floured counter and roll it into a rectangle. Mentally divide it into three parts; fold the bottom over the middle and the upper over the middle. Turn the dough 90° and repeat. Complete this folding process 5 times total.

Place the dough in the freezer for 5 minutes.

Heat a pan over medium heat, melt the butter, and add the apples, sugar, cinnamon, and lemon juice. Stir until softened and caramelized, no more than 5 minutes. Turn off the stove and let it sit. Optionally, add dark chocolate chips once the mixture cools slightly.

Preheat the oven to 400°F (200°C).

Roll the chilled pastry into a rectangle about 1/7 inch thick (optionally between two parchment papers to prevent sticking). Cut it into 6 rectangles.

Place the filling in the center of each rectangle, leaving the edges clean. Fold the pastry into a triangle and seal the edges with a fork.

Brush the turnovers with milk and sprinkle with a pinch of brown sugar and a pinch of ground cinnamon. Place them on a baking tray and cut 3 small diagonal slashes across the top of each pastry to let steam escape.

Bake for 15 to 20 minutes until caramelized but not too hard.

Remove from the oven and let cool for 15 minutes before serving.