Preheat your oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment, leaving overhang on the long sides for easy lifting. Lightly grease the exposed pan edges.
Make the crust: In a bowl, mix graham crumbs, sugar, melted butter, and a pinch of salt until the texture resembles wet sand.
Press firmly into the prepared pan in an even layer. Bake for 8–10 minutes, then set aside to cool slightly.
Prepare the cheesecake layer: Beat softened cream cheese and sugar on medium speed until smooth and fluffy, about 2 minutes. Add sour cream, eggs, vanilla, and salt.
Mix on low just until combined and silky. Do not overmix.
Make the apple layer: In a separate bowl, toss diced apples with brown sugar, cinnamon, lemon juice, and nutmeg if using. Set aside so the flavors meld.
Stir together the streusel: Combine oats, flour, brown sugar, cinnamon, and salt.
Cut in the cold butter with a pastry cutter or your fingers until clumps form. Stir in nuts if using.
Assemble: Pour the cheesecake batter over the slightly cooled crust and smooth the top. Scatter the spiced apples evenly over the cheesecake layer.
Sprinkle the streusel across the apples, covering most of the surface.
Bake for 35–40 minutes, until the edges are set and the center jiggles slightly when you nudge the pan. The streusel should look lightly golden.
Cool completely on a rack, then chill at least 4 hours, preferably overnight. Chilling sets the layers and makes slicing clean and easy.
Finish and serve: Lift the slab out using the parchment overhang.
Drizzle generously with caramel sauce. Add a tiny pinch of flaky sea salt if you like a sweet-salty contrast. Slice into bars and enjoy.