Preheat your oven to 425°F (220°C).
Prepare the apples by peeling, coring, and slicing them thinly, then place them in a large mixing bowl.
Add sugar, flour, cinnamon, nutmeg, and lemon juice to the apples. Stir until all the apples are evenly coated.
Roll out one pie crust and cut it to fit the bottom of the Mason jars.
Fill each jar with the apple filling, packing it down slightly to avoid gaps. Top with additional crust.
Cut slits in the top crust to create a vent. Brush the tops with beaten egg.
Place the jars onto a baking sheet and bake in the preheated oven for 25-30 minutes until the crust is golden.
Remove from the oven and let the jars cool for at least 10 minutes before serving.