Prepare the pie crust by mixing flour, salt, and sugar.
Cut in the butter until the mixture resembles coarse crumbs.
Add cold water slowly until the dough comes together.
Preheat your oven to 375°F (190°C).
Roll out the crust for the bottom layer and place it in a baking sheet.
Prepare the apple filling by combining sliced apples with sugars, cinnamon, cornstarch, and lemon juice.
Fill the crust with the apple mixture, fluffing it up.
Roll out the top crust and place it over the apple filling.
Brush the crust with the beaten egg.
Bake for 45-55 minutes or until the filling is bubbly and the crust is golden.
Let the pie cool before slicing.