In a medium bowl, whisk together the crumble topping ingredients: flour, brown sugar, cinnamon, and nutmeg. Add the cold, cubed butter and cut it into the mixture until it resembles coarse crumbs. Cover and refrigerate.

In another medium bowl, combine the diced apples, granulated sugar, lemon juice, cinnamon, nutmeg, and flour for the apple filling. Stir until evenly coated and set aside.

Preheat the oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.

In a large bowl, cream together the softened butter and granulated sugar until light and fluffy (3-5 minutes). Beat in the eggs one at a time, then stir in the vanilla extract.

In a small bowl, whisk together the sour cream (or yogurt) and milk. Gradually add the dry ingredients to the wet ingredients, alternating with the sour cream mixture, beginning and ending with the dry ingredients. Mix until just combined. Do not overmix.

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

Top each with about 2 tablespoons of the apple filling and sprinkle the crumble topping evenly over the apple filling.

Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean. Let cool in the muffin tin for a few minutes before transferring to a wire rack to cool completely.

Drizzle with caramel sauce and/or dust with powdered sugar before serving.