In a large mixing bowl, whisk together the flour and salt.
Add the chilled butter to the bowl and use a pastry cutter or your fingers to cut it into the flour until the mixture is crumbly.
Add the ice-cold water to the bowl and mix everything together until a dough forms.
Turn the dough out onto a lightly floured surface and knead it for a minute or two until it comes together in a smooth ball.
Wrap the dough in plastic wrap and refrigerate it for at least 30 minutes.
Roll the chilled dough out on a lightly floured surface into a rectangle about 1/4 inch thick.
Fold the bottom third of the dough up and the top third down, like a letter.
Turn the dough 90 degrees and roll it out again into a rectangle about 1/4 inch thick.
Fold the bottom third up and the top third down again.
Wrap the dough in plastic wrap and refrigerate it for at least 30 minutes.
Repeat steps 6-10 twice more, for a total of three folds.
Preheat your oven to 200°C.
In a medium mixing bowl, combine the chopped apples, brown sugar, cinnamon, nutmeg, cornstarch, lemon juice, and salt.
On a lightly floured surface, roll the chilled puff pastry dough out into a rectangle about 1/8 inch thick.
Use a knife or pizza cutter to cut the dough into squares or rectangles of equal size.
Spoon some of the apple mixture onto one half of each square or rectangle, leaving a little space around the edges.
Fold the other half of the dough over the filling and press the edges together with a fork to seal.
Place the turnovers on a baking sheet lined with parchment paper.
Bake the turnovers for 20-25 minutes, or until they are golden brown and crispy.
While the turnovers are baking, make the glaze by whisking together the powdered sugar, non-dairy milk, and vanilla extract in a small mixing bowl.
When the turnovers are done, let them cool for a few minutes before drizzling them with the glaze.
Serve the turnovers warm and enjoy!