Preheat the oven to 325°F (163°C). In a large mixing bowl, whisk together the graham cracker sheets, granulated sugar, and ground cinnamon. Drizzle in the melted unsalted butter and mix until crumbs are moistened. Divide into 18 muffin cups, pressing to create a base, and bake for 5 minutes.

In another bowl, whisk together all-purpose flour, quick oats, brown sugar, ground cinnamon, ground nutmeg, and salt. Cut in the cold butter until crumbles form. Chill until needed.

Toss the finely chopped apples with lemon juice. In a large bowl, beat the softened cream cheese with granulated sugar until smooth. Add eggs one at a time, then blend in sour cream and vanilla.

Pour ¼ cup of filling over each baked crust, top with the prepared apples, and sprinkle the streusel on top. Bake for 23-25 minutes until set at the edges but slightly jiggly in the center.

Cool at room temperature for 30 minutes, then refrigerate for at least 3 hours. Drizzle with salted caramel sauce before serving.