The original post gives some back story about this recipe. If you're curious why I choose to grate the apples, then it's definitely worth a read.
For the crumb topping:
For the muffins:
Preheat oven to 375º. Grease or line a 12-cup muffin tin with liners. For the topping, mix all the ingredients together in small bowl with a fork until it forms a wet, sandy mixture; set aside.
For the muffins, mix the flour, baking powder, baking soda, salt and all pice in a medium bowl; set aside. In a separate medium-sized bowl, beat the butter and sugar on medium-high speed until light and fluffy, about three minutes. Add the eggs one at a time, beating well after each one.
Beat in one third of the dry ingredients, then add one-third of the sour cream. Alternating between dry ingredients and sour cream, repeat until all ingredients have been incorporated. Using a wooden spoon or rubber spatula, stir in the apples.
Evenly spoon the batter into the prepared muffin tins. Sprinkle each muffin even with en equal amount of the crumb topping. Bake for 20 to 25 minutes, or until golden brown and a toothpick inserted comes out mostly clean—it's okay if there are a few dry crumbs.