01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly.
02 - In a large bowl, whisk together the flour, sugar, baking powder, baking soda, salt, and cinnamon.
03 - In a separate bowl, whisk together the eggs, vegetable oil, whole milk, and vanilla extract until smooth.
04 - Add the wet ingredients to the dry ingredients and stir gently until just combined; avoid overmixing.
05 - Fold the diced apples into the batter evenly.
06 - Divide batter evenly among muffin cups, filling each about three-quarters full.
07 - Mix granulated sugar and cinnamon in a small bowl, then sprinkle generously over each filled muffin cup.
08 - Bake for 18 to 22 minutes, or until a toothpick inserted in the center comes out clean.
09 - Cool in the pan for 5 minutes before transferring muffins to a wire rack to cool completely.