To begin, cover a baking sheet with aluminum foil and place it on the lowest rack of the oven. Pre-heat the oven to 425 degrees Fahrenheit (218 degrees Celsius).
For the Pie Filling:
Mix the lemon juice, zest, sugar, cornstarch, cinnamon, salt in a large bowl.
Peel, core, and slice apples into 1/4-1/2 inch pieces.
Toss apples into bowl with lemon sugar mixture.
Set apples aside to macerate while you prepare the crust.
To prepare the crust:
Add flour, butter, and cream cheese to a medium sized bowl and work the butter and cream cheese into the flour until the mixture resembles sand with small pebbles of butter and cream cheese throughout.
You can do this using a pastry cutter, two knives, or your hands.
Empty the flour, butter, cream cheese mixture on to a large piece of plastic wrap placed on a flat surface. Using your hands, lift the sides of the plastic wrap and begin to press the dough together until it comes together into a disk shape.
Wrap the dough in the plastic wrap and place it into the refrigerator for 45 minutes.
Transfer the apples into a 10 inch cast iron skillet and place it into the refrigerator for 45 minutes.
After 45 minutes, remove the pastry dough and the apples from the refrigerator.
Remove the dough from the plastic and place it on a flat floured surface. Flour a rolling pin and begin to roll out the dough from the center working to the outside. After each roll, move the dough a quarter turn to prevent it from sticking to the surface. If it does stick, pick up the dough and sprinkle the surface with additional flour. Roll the dough into approximately a 12-inch circle.
Carefully roll the dough onto the rolling pin and place it over the apples in the cast iron pan. Tuck the edges of the dough into the pan enveloping the apples.
Brush top of pie with egg and sprinkle on Demerara sugar.
Place the pie onto the aluminum foil covered baking sheet and bake the pie for 45-55 minutes until golden brown.
Allow pie to cool for 10 minutes, then scoop out and serve. Pie can also be served at room temperature or chilled for 1 hour and served cold. If storing pie leftovers, (if there are any!) transfer to a proper storage container and refrigerate. Do not store the pie in the cast iron pan as the liquid nature of the pie filling might adversely affect the seasoning of the pan.