Prepare Crumble Topping: In a medium bowl, whisk together the all-purpose flour, light brown sugar, ground cinnamon, and nutmeg until well combined. Cut in the cold unsalted butter until the mixture resembles coarse crumbs. Cover and refrigerate for 15 minutes.

Make Apple Filling: Chop the apples into small pieces, add granulated sugar, lemon juice, and a little flour, and toss until evenly coated. Set aside.

Prepare Cupcake Batter: Preheat oven to 350°F (175°C) and line muffin tin. In a mixing bowl, combine all-purpose flour, baking powder, baking soda, and salt.

Cream Butter and Sugar: In a separate bowl, cream softened unsalted butter with granulated sugar until fluffy. Beat in eggs one at a time and vanilla extract.

Combine Batter Ingredients: Gradually add the dry mixture to creamed mixture, alternating with sour cream and milk until combined.

Assemble and Bake: Fill cupcake liners, add apple filling, sprinkle crumble topping, and bake for 20-25 minutes or until a toothpick comes out clean.

Garnish and Serve: Cool in the pan for 10 minutes, then transfer to a wire rack. Drizzle with caramel sauce or dust with powdered sugar before serving.