Preheat oven to 400°F. Grease muffin tin or use paper liners.
Make the topping:
In the bowl of a food processor, pulse the topping ingredients of sugar, flour, butter and cinnamon until fully blended and has the consistency of small crumbs. set aside.
Make the batter:
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium speed until light and fluffy. Add the eggs, beating until incorporated. Add the vanilla and cinnamon and beat until just mixed in.
In a large bowl, whisk together the flour, baking powder and salt.
Add the flour mixture and milk to the butter mixture until just combined. Scrape down the sides of the bowl as needed. The dough will be thick. Fold the apples into the muffin batter until well distributed.
Using an ice cream scoop or spoon, fill muffin cups with batter 3/4 full. Divide the crumb topping mixture equally between muffins, completely covering the muffin batter.
Place muffin pan on center rack of oven and bake for 20 - 25 minutes, or until knife stuck into center of muffin comes out clean.
Place pan with muffins on cooling rack for 10 minutes before removing muffins from pan.