Preheat oven to 375°F. Prepare muffin tins with flour and butter, discarding excess flour or use muffin tin liners. Set aside.
In a medium bowl, sift together 2 cups flour, baking powder, salt, and 2 teaspoons cinnamon. Set aside.
In a small bowl, mix 2 teaspoons flour with ½ tsp cinnamon. Sprinkle over diced apples in a separate bowl, stir to coat and set aside.
In a large bowl using a mixer, cream together butter and sugar until lightened in color. Add eggs one at a time, fully incorporating before adding the next. Mix in vanilla extract.
Alternating between flour mixture and milk, stir in ingredients until combined. Fold in diced apples, careful not to overmix. Scoop mixture into prepared muffin tin, about ¾ full. Bake 16-20 minutes, until tester comes out clean.
To make topping, melt butter in a small bowl. In separate small bowl whisk together sugar and cinnamon. Dip or brush the top of muffins with butter, then dip in cinnamon sugar. Place onto cooling rack and enjoy!