1. In a medium bowl, whisk together the flour, brown sugar, cinnamon, and nutmeg for the crumble topping.

2. Add the cold cubed butter and cut it into the flour mixture using a pastry blender or your fingertips until it resembles coarse crumbs.

3. Cover and refrigerate the crumble topping.

4. In a medium bowl, combine the diced apples, granulated sugar, lemon juice, cinnamon, nutmeg, and flour.

5. Stir until evenly coated, then set the apple filling aside.

6. Preheat the oven to 350 degrees Fahrenheit and line a 12-cup muffin tin with cupcake liners.

7. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt for the cupcake batter.

8. In a large bowl, cream together the softened butter and granulated sugar until light and fluffy, about 3 to 5 minutes.

9. Beat in the eggs one at a time, then stir in the vanilla extract.

10. In a small bowl, whisk together the sour cream or yogurt and milk.

11. Gradually add the dry ingredients to the butter mixture, alternating with the sour cream mixture, beginning and ending with the dry ingredients.

12. Mix until just combined, being careful not to overmix.

13. Spoon about 2 tablespoons of cupcake batter into each cupcake liner.

14. Top each cupcake with about 2 tablespoons of apple filling.

15. Sprinkle the crumble topping evenly over the apple filling.

16. Bake for 20 to 25 minutes, or until a toothpick inserted into the center comes out clean.

17. Let the cupcakes cool in the muffin tin for a few minutes, then transfer to a wire rack to cool completely.

18. Drizzle with caramel sauce and dust with powdered sugar before serving, if desired.