Preheat the oven to 375°F (190°C). Line a muffin tin with paper liners and place all ingredients and tools within reach before starting.
Whisk together flour, baking powder, cinnamon, baking soda, and salt in a medium bowl until evenly combined.
Whisk eggs, milk, maple syrup or honey, oil, and vanilla extract in another bowl until smooth. Fold in the diced apples.
Pour the wet mixture into the dry ingredients. Fold gently with a spatula until the flour disappears. Avoid overmixing because it can make muffins dense.
Divide the batter evenly into the muffin liners, filling each cup about ¾ full. Sprinkle the cinnamon topping over each muffin if desired.
Bake for 18–22 minutes until the tops are golden and a toothpick inserted in the center comes out with a few moist crumbs.
Leave muffins in the pan for 5 minutes, then transfer them to a cooling rack for another 15 minutes before eating.
Keep cooled muffins in an airtight container at room temperature for up to 3 days or freeze for up to 3 months.
