Preheat the oven to 400°. Grease a 12-cup muffin tin with butter or non-stick cooking spray or use paper liners.
In a large mixing bowl, combine both flours, baking powder, cinnamon, and salt. Blend well with a whisk. Add the diced apples. Stir to combine.
In a medium mixing bowl, combine the oil, brown sugar, eggs, vanilla extract, and milk.
Pour the wet ingredients into the dry and mix with a spoon, just until combined.
Divide the batter evenly among the 12 muffin cups.
Bake muffins for 13–16 minutes until golden on top and a toothpick inserted in the center comes out clean.
