For Crumb Topping
1/2 cup all purpose flour
Preheat oven to 375º. Grease or line a 12-cup muffin tin with liners. For the topping, mix all ingredients in small bowl with a fork until combined; set aside.
For the muffins, mix flour, baking powder, baking soda, salt and all spice in a medium-size bowl; set aside. In a medium-sized bowl, cream butter and sugar on medium-high speed until light and fluffy, about three minutes. Add 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 diced apples.
Evenly divide batter into the muffin-tin cups. Sprinkle tops evenly with the crumb topping. Bake for 20 to 25 minutes, or until golden brown and toothpick inserted comes out clean.