Prep the muffin tin: Line a 12-cup muffin tin with paper liners and preheat the oven to 325°F. This keeps the cheesecakes from sticking and makes cleanup easy.

Make the crust: Mix graham cracker crumbs with 3 tablespoons melted butter until it looks like wet sand. Press about a tablespoon into the bottom of each liner, packing it firm with a spoon or your fingers.

Beat the cream cheese: Beat the cream cheese and granulated sugar together until completely smooth, scraping down the bowl once or twice. This keeps the filling free of lumps.

Add eggs and vanilla: Add the eggs one at a time on low speed, mixing just until combined after each. Stir in the vanilla extract, being careful not to overmix and add too much air.

Fill and bake: Divide the batter evenly over the crusts, filling each liner about three-quarters full. Bake for 16-18 minutes, until the edges are set but the centers still jiggle slightly.

Cook the apples: While the cheesecakes bake, melt 2 tablespoons butter in a skillet over medium heat. Add the diced apples, 2 tablespoons brown sugar, 1/2 teaspoon cinnamon, and nutmeg, and cook for 6-8 minutes until softened and syrupy.

Mix the crumble: In a small bowl, combine the oats, flour, remaining brown sugar, remaining cinnamon, and cold cubed butter. Use your fingers to rub it together until it forms coarse, pea-sized crumbs.

Cool gradually: Turn off the oven and crack the door open, letting the cheesecakes sit inside for 10 minutes. This slow cooling helps prevent the tops from sinking or cracking.

Top with apples and crumble: Once cooled to room temperature, spoon the cinnamon apples over each cheesecake and sprinkle generously with the oat crumble.

Chill before serving: Refrigerate the mini cheesecakes for at least 2 hours, or until fully set and firm. Serve cold, straight from the liners.