Preheat your oven to 350°F and line a 12-count muffin pan with cupcake liners or spray generously with non-stick cooking spray.
In a medium bowl whisk the flour, baking powder, baking soda, salt, and cinnamon.
In a larger bowl whisk the melted butter, granulated sugar, brown sugar, eggs, vanilla, and milk. Add the dry ingredients to the wet ingredients and whisk until smooth.
Fold the diced apples into the batter and add to the prepared muffin pan, filling all the way to the top. Sprinkle the tops with a little brown sugar and bake for 22-23 minutes. A toothpick inserted into the center should come out clean.