Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, salt, and cinnamon.
In another bowl, whisk the eggs, melted butter, milk, and vanilla extract until combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
Fold in the chopped apple.
Divide the batter evenly among the muffin cups.
Bake for 20 minutes or until a toothpick inserted into the center of a muffin comes out clean.
Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.