Make the Cupcake Batter

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper cupcake liners.
2. Mix Dry Ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, and salt. Set aside.
3. Cream the Butter and Sugar: In a large mixing bowl, beat the softened butter and brown sugar together until light and fluffy. This should take about 3 minutes.
4. Add the Eggs and Vanilla: Beat in the eggs one at a time, making sure each is fully incorporated before adding the next. Stir in the vanilla extract.
5. Alternate Adding Dry Ingredients and Buttermilk: Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk. Start and finish with the dry ingredients, mixing until just combined.
6. Fold in the Apples: Gently fold in the chopped apples, making sure they are evenly distributed throughout the batter.
7. Fill the Cupcake Liners: Spoon the batter into the cupcake liners, filling each about two-thirds full.

Make the Streusel Topping

1. Mix Streusel Ingredients: In a small bowl, combine the flour, brown sugar, cinnamon, and butter. Use your fingers or a fork to work the butter into the dry ingredients until the mixture becomes crumbly.
2. Top the Cupcakes: Sprinkle a generous amount of streusel topping over each cupcake, pressing lightly to adhere.

Bake the Cupcakes

1. Bake: Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until a toothpick inserted into the center of a cupcake comes out clean.
2. Cool: Let the cupcakes cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.