Peel, core, and cut the apples into ½-inch pieces. Place cut apples into a large bowl filled with water (to prevent browning).
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.
Preheat oven to 425F.
On a lightly floured surface, roll out pie crusts & cut into 10 circles.
Place ⅓ cup of apple filling at the center of each circle. Fold over the dough, leaving a ½-inch overlap. Push down with a fork to seal the filling.
Transfer hand pies onto a parchment-lined baking tray.
Brush egg generously on the top surface and sprinkle some sugar on top (optional).
Cut slits in the top and bake for 12 minutes, until pastry is golden brown.