Pastry Dough:

1. Add flour, sugar, salt and butter into a food processor. Pulse on and off until flour mixture forms into small pieces of dough, approximately 1 minute.
2. Drizzle ice water into the mixture (ice water is the key). Close the lid and continue to pulse on and off for another 1 minute, until the dough turns into a breadcrumb consistency.
3. Transfer dough (breadcrumbs consistency) on a work surface. Use your hands to squeeze all the pieces together until it forms into a dough. Shape it into a smooth disc. Wrap the disc in plastic wrap and refrigerate for 1 hour.

Apple Filling:

1. Peel, core and cut the apples into 1/2-inch cubes. Place apples into a large bowl filled with water (to prevent browning).
2. In a saucepan, melt butter over medium heat. Stir in apples, sugar, cinnamon, brown sugar, and salt. Cover and stir occasionally for 5 minutes or until apples are slightly softened. Stir in flour and continue to cook until apples are soft and tender (but not mushy), and the filling has thickened. Remove from heat and cool to room temperature.

Assembling and Baking Apple Turnovers:

1. Preheat oven to 400 F.
2. On a lightly floured surface, roll out dough to 1/8-inch thickness (or the thickness of a cardboard box). Cut out dough into 6-inch circles.
3. Place 1/3 cup of apple filling at the centre of each circle. Fold over the dough, leaving 1/2-inch overlap. Push down to seal the filling. Fold over the overlap and press down to seal the edge.
4. Crimp the edges using a your fingers or a fork (see photos above in post). Transfer turnovers onto a parchment-lined baking tray.
5. Brush egg generously on the top surface and sprinkle some sugar on top (optional). Cut out three small ventilation holes on top of the turnover. Bake for 25-30 minutes, until pastry is lightly browned.