Preheat the oven to 350 degrees F. Dice the apple using a cutting board and large sharp knife. Set aside.
Place the maple syrup and the softened butter in a large bowl and stir with a hand mixer, or use a stand mixer, until well combined, scraping the sides with a spatula as necessary.
In a separate bowl, combine the flour, baking soda, baking powder, cinnamon, nutmeg, and salt. Stir to combine. Set aside.
Stir the eggs, applesauce, and vanilla extract into the maple syrup & butter mixture until well combined, then pour the wet mixture into the bowl with the dry mixture. Stir until just combined and there are no pockets of dry flour in the mixture. Pour the diced apple into the batter and gently stir until they are evenly distributed.
Scoop the muffin mixture into each well in the silicone muffin pan with a spoon, dividing it equally between each well. Place the muffin pan onto a sheet pan and into the oven, setting the timer for 15 minutes. After the timer goes off, carefully rotate the muffin pan 180 degrees (so the muffins in the front of the oven are now in the back of the oven) and bake for another 10 minutes.
Insert a toothpick into one or two muffins to check for doneness after timer goes off. If not done, cook until a toothpick inserted into the middle of a muffin comes out clean (another 2 to 4 minutes). Once cooked, take the muffins out of the oven and let cool for 5 to 10 minutes.
Measure out the sugar and cinnamon into a bowl with a flat bottom. Stir until they're combined. Use a pastry brush to brush a small amount of butter on top of one of the muffins, just enough to cover it. Pick up the muffin and dip the top into the cinnamon sugar mixture. Roll the top around in it until it's fully covered. Repeat with each muffin until they're all covered in a cinnamon sugar topping.