Preheat oven to 425°F and prepare a 6-slot jumbo muffin tin with liners and set aside.
Whisk together the flour, baking soda, baking powder, salt, and cinnamon in a medium-sized bowl. Set aside.
Whisk together the melted butter, brown sugar, granulated sugar, eggs, and vanilla in a large bowl. Then, add in the sour cream and apple sauce and whisk until smooth.
Add the apples to the batter and fold them in with a rubber spatula.
Make the crumb topping. Combine the brown sugar, cinnamon, melted butter, and flour in a medium-sized bowl. Mix with a fork to form the crumbs.
Add batter to the muffin tin and fill all the way to the top. Generously top each muffin with the crumb topping.
Bake muffins at 425°F for 5 minutes and turn the heat down on the oven to 350°F while the muffins are in the oven. Continue to bake for 25-30 minutes, until the muffins are fully browned on top and a toothpick can run clean through them.
Let muffins slightly cool for about 10 minutes in the pan before taking them out.
