Mix Dry Ingredients: In a large mixing bowl, whisk together the flour, sugar, cinnamon, baking powder, baking soda, and salt until well combined.
Mix Wet Ingredients: In a separate mixing bowl, add the eggs, applesauce, oil, and vanilla; whisk until smooth. Add melted butter and whisk to combine.
Add Wet to Dry: Pour the wet mixture into the dry mixture and gently fold with a spatula or whisk until just combined, leaving some streaks of flour visible.
Fold in Apple: Add the chopped apple and gently fold it into the batter until evenly distributed.
Rest Batter: Cover the bowl with plastic wrap or a tea towel and let the batter sit at room temperature for 1 hour to allow the flour to fully hydrate for a taller, fluffier muffin. Preheat the oven to 400ºF (200ºC) about 30 minutes into this resting time and line a 12-hole muffin/cupcake tin with paper liners, set aside.
Prepare Cinnamon Sugar Topping: While the batter rests, mix together the cinnamon and granulated sugar in a small bowl until combined. Set aside.
Fill Muffin Tin: Spoon the batter into the lined muffin cups, slightly overfilling each one to achieve a tall rise (refer to images in the blog post for guidance). This recipe should make 12 muffins. Sprinkle the cinnamon sugar mixture generously over the tops of each muffin.
Bake: Bake for 5 minutes, then reduce the oven temperature to 180ºC (350ºF) and bake for an additional 10-13 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Cool: Let the muffins cool in the pan for 5 minutes before transferring to a wire rack to cool completely.