First, heat your oven to 350°F and lightly grease the pie dish so your crust doesn’t stick. In a large bowl, combine the snickerdoodle mix with softened butter, using a pastry blender or fork until the mixture resembles coarse crumbs. Press about 2 cups of this into the bottom and up the sides of your pie plate; this forms the sweet cookie crust. Bake the crust for about 10 minutes until lightly golden, then set it aside to cool.
Beat the softened cream cheese in a medium bowl until smooth. Add the sugar and flour, mixing thoroughly. Stir in vanilla extract and the egg, then continue beating until the filling is silky and well combined. This creamy layer adds a delicious tang that balances the sweet apple topping.
In a small bowl, toss chopped apple pie filling with cinnamon until evenly coated. Spread the cream cheese mixture into the cooled crust, then spoon the cinnamon‑spiced apples on top, aiming for more fruit than syrup. Sprinkle the reserved snickerdoodle crumb mixture evenly over the apples to create a crunchy finish.
Bake your assembled pie at 350°F for about 35 minutes, or until the top is a lovely golden brown and you can smell the warm cinnamon. Let the pie cool completely, then refrigerate for at least 3 hours so it sets properly and slices cleanly.