Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners.
In a large bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.
In another bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined. Add the eggs and vanilla extract, and whisk until smooth.
Gradually add the dry ingredients to the wet ingredients, alternating with the milk. Mix until just combined. Fold in the chopped apples.
Divide the batter evenly among the muffin cups, filling each about ⅔ full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Allow the muffins to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.