Preheat the oven to 350° F. Grease a standard muffin tin or line with paper liners; set aside.
In a large bowl, whisk the applesauce, egg, oil, sugars, and buttermilk together until well combined.
1 cup unsweetened applesauce, 1 large egg, ⅓ cup neutral oil, ½ cup granulated sugar, ¼ cup brown sugar, ¾ cup buttermilk
Add the flour, baking powder, baking soda, apple pie spice, and salt. Whisk in just until combined.
2 cups all purpose flour, 1 ½ teaspoons baking powder, ½ teaspoon baking soda, 2 teaspoons apple pie spice, ½ teaspoon salt
Divide the batter among the prepared muffin tins, filling about ⅔ to ¾ full.
Sprinkle with sparkling sugar.
Bake for about 18-25 minutes or until a toothpick inserted into the center of a muffin comes out clean.
Let the muffins cool in the pan for about 5 minutes before transferring to a wire rack to cool.
Notes
Applesauce: I use unsweetened applesauce; however, you could use sweetened applesauce if you want sweeter muffins.
Oil: I like to use olive oil in these muffins, but other neutral oils, like canola oil, also work.
Buttermilk: Regular or low-fat buttermilk will work. If you don't have buttermilk, you can make a homemade buttermilk substitute.
Flour: You could substitute half whole-wheat flour for the all-purpose flour if you would like.
Apple pie spice: I think the apple pie spice adds a nice depth of flavor. You could use ground cinnamon if you prefer. Feel free to adjust the amount according to your tastes.