Preheat oven to 400°F. In a large bowl, combine the flour, baking powder, baking soda, and salt, then set aside.
In a separate bowl, whisk together the melted butter and sugars.
Whisk the milk, eggs, and vanilla extract into the butter mixture until well combined.
Fold in the dry ingredients, mixing until just combined.
Fold in the apples and cinnamon.
Line a 12-count muffin tin with paper liners or grease heavily. Fill each muffin cup ¾ full.
Bake in the preheated oven for 5 minutes, then turn the temperature down to 350°F. Bake for 16-17 more minutes until the centers are completely set, verified with a toothpick inserted in the center.
Allow the muffins to cool, then serve!