Preheat the Oven and Prepare the Muffin Tin:
Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or lightly grease the cups with cooking spray.
Mix the Dry Ingredients:
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Set aside.
Cream the Butter and Sugar:
In a large bowl, beat the softened butter and sugar together until light and fluffy, about 2-3 minutes.
Add the Wet Ingredients:
Add the eggs and vanilla extract to the butter mixture. Beat until smooth and fully combined.
Add the Dry Ingredients to the Wet Ingredients:
Gradually add the dry ingredients to the wet ingredients, mixing just until combined. Be careful not to overmix.
Add the Buttermilk and Apples:
Slowly add the buttermilk to the batter and stir until just incorporated. Gently fold in the diced apples.
Fill the Muffin Tin:
Spoon the batter into the muffin cups, filling each about 2/3 full. Use a spoon or ice cream scoop to make this process easier.
Make the Cinnamon Sugar Topping:
In a small bowl, mix together the cinnamon and sugar. Sprinkle this mixture evenly over the tops of the muffins.
Bake the Muffins:
Bake in the preheated oven for 18-22 minutes, or until a toothpick inserted into the center of a muffin comes out clean. The tops should be golden brown.
Cool the Muffins:
Once baked, allow the muffins to cool in the tin for a few minutes. Then transfer the muffins to a wire rack to cool completely.