Preheat your oven to 375°F (190°C). Prepare a 12-cup muffin tin by lining it with paper liners or spraying it with non-stick cooking spray.

In a large mixing bowl, combine the all-purpose flour, baking powder, baking soda, ground cinnamon, and salt. Whisk thoroughly until well combined.

In a separate bowl, whisk together the large eggs, melted unsalted butter, granulated sugar, milk, and vanilla extract until smooth.

Pour the wet mixture into the bowl with the dry ingredients. Gently mix until just combined and fold in the peeled and diced apples.

Divide the batter evenly among the muffin cups, filling each about three-quarters full. Sprinkle turbinado sugar over the batter if desired.

Bake for 18-20 minutes. When a toothpick inserted comes out clean, remove the muffins from the oven.

Allow muffins to cool in the pan for about 5 minutes before transferring them to a wire rack.