Preheat oven to 450.
Peel, core, and chop your apples.
Combine your dry ingredients in a bowl and set aside.
In a seperate bowl, cream your butter and sugars.
Mix in your eggs.
Gently mix in your buttermilk. Overmixing buttermilk can cause curdling.
Mix in dry ingredients.
Fold in chopped apple.
Add muffin liners and fill muffin tray with mixture. Use an ice cream scoop to save time and have uniform shapes and sizes.
Lastly, top muffins with brown sugar to add the crunchy goodness. The amount of sugar is really up to your discretion. See note for further explaination.
Bake for 10 minutes at 450.
Then turn heat down to 400 and bake for another 5-10 minutes.
Cool muffins in pan for approxiately 5 minutes.
Place on wire rack to cool completely.