Preheat the oven to 375F degrees and line a muffin pan with papers.
In a large bowl beat the butter, white sugar & brown sugar until fluffy.
Mix in the eggs 1 at a time, then the vanilla.
In a separate bowl whisk together the flour, 1 teaspoon cinnamon, baking powder, baking soda & salt.
With the mixer on low speed beat about 1/3 of the flour mixture into the butter mixture, alternating with about 1/3 of the milk. Repeat the process until everything is combined.
In a separate bowl toss the chopped apple with the 1/2 teaspoon cinnamon.
Gently fold the chopped apple into the muffin batter using a large rubber spatula or wooden spoon.
Spoon the batter into the prepared muffin pan - you'll get about 12 muffins total.
In a small bowl stir the sugar and cinnamon for the cinnamon sugar topping together. Then sprinkle it on top of each muffin.
Bake in the preheated oven for 17-20 minutes, or until the tops are golden and an inserted toothpick comes out clean.
*Muffins are best if eaten the same day they're made. Store muffins in an airtight container for up to 4 days.