In a mixing bowl, combine graham cracker crumbs, melted unsalted butter, and brown sugar until fully moistened. Press this mixture firmly into the bottom of a 9-inch springform pan, creating an even layer.

In a large bowl, beat the cream cheese with an electric mixer until smooth and creamy, about 3 minutes. Gradually mix in granulated sugar, sour cream, and vanilla extract until fully combined. Add the eggs one at a time, mixing on low speed.

To prevent the cheesecake from cracking, place the springform pan inside a larger roasting pan. Fill the outer pan with hot water halfway up the sides of the springform pan.

Preheat oven to 325°F. Bake the cheesecake for 60-70 minutes until the center jiggles slightly. Turn off the oven, crack the door open, and let it cool for 1 hour.

While cooling, peel and dice apples, toss with lemon juice. Combine apples with brown sugar, cinnamon, nutmeg, flour, oats, and cubed butter. Mix into coarse crumbs.

Spread apple mixture onto a baking sheet and bake at 350°F for 20 minutes. Let cool completely.

Once cheesecake has cooled to room temperature, transfer to the refrigerator and chill for at least 4 hours or overnight.

When ready to serve, remove the cheesecake from the fridge and release it from the springform pan. Spoon the cooled apple crisp topping over the cheesecake.