In a large bowl, mix the flour, granulated sugar, and salt together. Then, add the butter and shortening. Using a pastry cutter or fork, cut them into the dry ingredients until they resemble a coarse meal.
Slowly drizzle in one tablespoon of ice water at a time and gently mix it in until the dough starts to come together with a fork. Do not add any more water than you need to. Stop adding water when the dough begins to form large clumps.
Divide the dough in half and pack the dough into a ball. Cover each one tightly with plastic wrap and finally refrigerate for at least 2 hours.
Apple Filling
In a small bowl, combine cornstarch and water until well combined. Set aside.
Preheat a large skillet over medium heat. Melt the butter completely. Add the diced apples and cook until they soften for about 4-5 minutes while stirring occasionally.
Reduce the heat to low and stir in brown sugar, cinnamon powder, and nutmeg powder until well combined. Stir in cornstarch slurry until the sauce thickens. Turn off the heat and let it cool completely before using. Set aside.
Egg Wash
In a small bowl, mix together egg and milk until incorporated.
Assembly
Preheat oven to 375F/190°C. Line two baking pans with baking mats or parchment paper.
Lightly dust the working surface lightly with flour. Then, roll one of your pastry dough out to about 1/8-1/4-inch/3-5mm thick. At any sign of sticking, sprinkle some flour underneath then keep rolling. One half of the dough is for the bases and the other half is for the tops. Using a 3.5-inch/9 cm cookie cutter, cut into circles (these are the bottom crust). Re-roll any scraps and cut them into circles.
Add about 1 tablespoon of the apple pie filling to the center of each circle. Brush the edges with egg wash.
Lattice top. Roll the remaining pastry dough out to about 1/8-1/4-inch/3-5mm thick. Cut the dough into 1/2-inch/1.2cm strips with a knife. Arrange the lattice on top of each circle. Cut and remove excess with the same round cutter you used for the base.
Closed Pies. Roll the remaining pastry dough out to about 1/8-1/4-inch/3-5mm thick. Using a 3.5-inch/9cm cookie cutter, cut into circles (these are the top crust). Arrange the circles on top. Press your fingers all around the edges to seal. Using a sharp knife, cut slits on top.
Crimp the edges with a fork.
Brush the top with egg wash and sprinkle with coarse sugar.
Bake for about 28-32 minutes or until they are golden brown. Rotate pans halfway through baking. Remove from the oven and allow them to cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool until ready to handle.