Preheat your oven to 400°F. While preparing and cooling the apple filling, thaw the puff pastry sheets as directed on the package.

In a medium-sized pot, melt 1 Tbsp butter over medium heat. Add the diced apples, cooking and stirring occasionally until they soften (around 5 minutes).

Lower the heat, then stir in the brown sugar, cinnamon, and salt. Let it simmer for 3 more minutes until the apples are tender and caramelized. Remove from heat and allow the mixture to cool.

Roll out the first thawed pastry sheet into an 11-inch square using a rolling pin. Cut this into 4 equal squares using a pizza cutter. Place the cooled apple mixture onto one half of each square, ensuring there is a 1/2-inch border.

In a small bowl, beat the egg and water together. Brush this egg wash lightly around the edges of the pastry squares. Fold the pastry over the apple filling and press the edges together firmly with a fork to seal. Repeat with the second pastry sheet to make 8 turnovers in total.

Place the turnovers on a baking sheet lined with parchment paper, ensuring they are spaced at least 1 inch apart. Use a paring knife to cut 2-3 small slits in the top of each turnover. Brush the tops with the remaining egg wash and bake for 20-23 minutes, until golden and puffed.

While the turnovers are still warm, mix the powdered sugar and heavy cream to your desired consistency and drizzle over the turnovers.