Prepare the Crust: In a medium bowl, combine the graham cracker crumbs, melted butter, and sugar. Press the mixture firmly into the bottom of a 9×13 inch baking pan lined with parchment paper.
Bake the Crust: Bake the crust in a preheated oven at 350°F (175°C) for 8 minutes. Let it cool slightly while you prepare the cheesecake filling.
Make the Cheesecake Filling: In a large bowl, beat the softened cream cheese and sugar until smooth and creamy.
Add Eggs and Flavorings: Beat in the eggs one at a time, then stir in the vanilla extract and sour cream.
Pour Filling Over Crust: Pour the cheesecake filling evenly over the cooled crust. Use a spatula to smooth the surface.
Prepare the Apple Crisp Topping: In a separate bowl, combine the diced apples, flour, brown sugar, oats, cold cubed butter, cinnamon, and nutmeg. Use your fingers or a pastry blender to cut the butter into the dry ingredients until the mixture resembles coarse crumbs.
Sprinkle Topping: Sprinkle the apple crisp topping evenly over the cheesecake filling.
Bake the Cheesecake: Bake in the preheated oven for 35-40 minutes, or until the cheesecake is set and the topping is golden brown.
Cool Completely: Let the cheesecake cool completely in the pan on a wire rack. Then, cover and refrigerate for at least 4 hours, or preferably overnight, before cutting into squares.
