Preheat oven to 375Mix wet and dry ingredients in separate bowls- tossing apple pieces in flour in dry ingredients. WET Ingredient bowl: Cream together the butter and sugars until light and fluffy- add eggs, milk,vanilla and sour cream. Dry Ingredient: flour, baking powder, salt, cinnamon, apples. The topping is mixed in a small bowl and set aside. Combine wet and dry ingredients and mix only until combined- DO NOT overmix. Fill muffin tins with batter (mini or regular) and top with crumble. Bake until a tooth pick can be pulled out with just crumbs on it- no wet batter. Depending on size of muffin 15-30min- For bake times you need to really figure out on your own as your oven temp may not be the same as mine. I rarely like to give bake times at all. Set timer for 15 min and check. Then 5 min intervals after that.