Prep the Pan: Line the bottom of a 9-inch springform pan with parchment and lightly grease the sides.
Wrap the outside in two layers of heavy-duty foil to prevent leaks if using a water bath.
Make the Crust: Mix graham crumbs, sugar, cinnamon, salt, and melted butter until it resembles wet sand. Press firmly into the bottom and slightly up the sides of the pan. Bake at 350°F (175°C) for 8–10 minutes, then cool slightly.
Reduce oven to 325°F (165°C).
Season the Apples: Toss sliced apples with brown sugar, cinnamon, nutmeg, lemon juice, and cornstarch (if using). Set aside to let the juices start releasing.
Stir Together the Streusel: Combine oats, flour, brown sugar, cinnamon, and salt. Cut in the cold butter with your fingers or a pastry cutter until clumpy and crumbly.
Refrigerate while you make the filling.
Beat the Cheesecake Filling: In a large bowl, beat cream cheese on medium speed until completely smooth and no lumps remain. Add sugar and salt; mix until silky. Beat in sour cream, vanilla, and lemon juice.
Mix in flour. Add eggs one at a time on low speed, just until combined. Do not overmix.
Assemble the Layers: Pour half the cheesecake batter into the cooled crust. Arrange half the apples in an even layer.
Add the remaining batter, then top with the rest of the apples. Sprinkle the chilled streusel evenly over the top.
Prepare for Baking: For the most even texture, place the pan in a larger roasting pan and pour in hot water to come halfway up the sides of the springform. If you skip the water bath, place a pan of hot water on the lower rack to add moisture.
Bake: Bake at 325°F (165°C) for 60–75 minutes.
The edges should be set and lightly puffed, with a slight wobble in the center. If the streusel browns too quickly, tent loosely with foil for the last 15 minutes.
Cool Gradually: Turn off the oven and crack the door. Let the cheesecake rest inside for 45–60 minutes.
This slow cool helps prevent cracks.
Chill: Move to a wire rack until close to room temperature, then refrigerate for at least 6 hours, preferably overnight. Don’t remove the springform ring until fully chilled.
Serve: Release the ring, slice with a hot, clean knife, and drizzle with warm caramel if you like. Add a dollop of whipped cream for an extra treat.