Preheat oven to 400° F. Prepare a muffin tin with paper liners and set aside. Make the crumble by whisking together the flour, brown sugar, sugar and cinnamon. Pour in melted butter.
Mix until small clumps form.
In a medium bowl, whisk together the flour, baking powder, salt and cinnamon. Set aside.
Add eggs, sour cream, and vanilla. Mix until combined.
Add half the flour mixture and mix just until combined. Add the milk and mix again. Add in the remaining flour mixture and mix until combined.
Stir in the diced apples by hand.
Divide batter among prepared muffin cups, filling each cup three-quarters full.
Bake at 400° F for 20 minutes or until a toothpick inserted in the center comes out with little to no crumbs. Allow muffins to cool in the pan for a few minutes before transferring to a wire rack to cool completely.
Store the muffins in an airtight container at room temperature for up to three days.