Preheat oven to 375º F. Spray muffin tins with cooking spray or place 12 silicon muffins cups on a baking sheet
Combine 2 cups flour, baking powder, salt, and 2 teaspoons cinnamon in a medium bowl. Set aside.
Peel and dice apples. Two cups is about 2 medium apples. Toss diced apples with 2 tsp flour and 12 tsp of cinnamon and set aside.
Cream butter and sugar until thoroughly mixed. Add eggs and mix thoroughly. Mix in vanilla.
Gently fold in half the flour mixture and then half the milk. Repeat with remaining flour and milk. Stir until just combined. Fold in diced apples. Using a large cookie scoop fill muffins tins or silicon cups until nearly full.
Bake until a toothpick or skewer inserted in the middle comes out clean, about 30 minutes.
Prepare topping for muffins: Melt butter. Combine sugar and cinnamon.
Once muffins have baked, remove from the oven and allow to cool slightly in the muffin tin. Then brush each muffin with butter using a pastry brush and sprinkle with cinnamon sugar mixture. Place onto a plate to finish cooling.