Preheat the oven to 350?F (175?C) and grease a muffin tin.

In a mixing bowl, whisk together the dry ingredients: flour, baking powder, baking soda, salt, and cinnamon.

In another bowl, mix the wet ingredients: granulated sugar, brown sugar, egg, milk, vegetable oil, and vanilla extract until well combined.

Gradually add the wet mixture to the dry ingredients, stirring until just combined.

Fold in the diced apples.

Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full.

Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted into the center comes out clean.

Allow to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.