Preheat your oven to 325°F (163°C) and prepare a 9-inch springform pan. Grease the sides and wrap the base in foil to prevent any leakage during baking.

In a mixing bowl, combine the graham cracker crumbs, granulated sugar, and melted unsalted butter. Stir until the crumbs are evenly coated with butter. Press this mixture firmly into the bottom of the prepared pan.

Bake the crust for 8-10 minutes, until it begins to set and turn a light golden brown.

While the crust cools, prepare the apple filling by tossing the peeled and diced apples with brown sugar, cinnamon, flour, and lemon juice in a separate bowl.

In another bowl, beat the softened cream cheese and granulated sugar together until smooth.

Add the eggs to the cream cheese mixture one at a time, mixing well after each addition. Stir in the vanilla extract, sour cream, cinnamon, and nutmeg.

Pour the creamy cheesecake filling over the cooled graham cracker crust.

Spoon the apple mixture over the cheesecake layer.

To make the crumb topping, mix together the old-fashioned oats, flour, brown sugar, and cinnamon. Cut in the cold, cubed butter until the mixture resembles coarse crumbs.

Sprinkle the crumb mixture over the apple layer.

Place the springform pan in a larger baking dish filled with water (a water bath) and bake for 60-70 minutes.

Once baked, turn off the oven and let the cheesecake cool in the oven for 1 hour.

After cooling in the oven, refrigerate the cheesecake for at least 4 hours or overnight.