Heat the oven to 350°F. Line a 12-cup muffin tin with parchment paper muffin liners. Very lightly spray each muffin liner with nonstick cooking spray.
In a large mixing bowl, add the granulated sugar, light brown sugar, oil, and large egg. Stir with a wire whisk until it's thoroughly combined and darker in color.
1/3 cup granulated sugar, 1/3 cup packed light brown sugar, 1/3 cup vegetable oil, 1 large egg
Add the applesauce, sour cream, milk and vanilla extract and whisk until combined.
1 cup applesauce, 1/4 cup full-fat sour cream, 2 tablespoons whole milk, 1 teaspoon vanilla extract
Add in the flour, baking powder, ground cinnamon, and salt. Use a wooden spoon or rubber spatula to gently mix until combined and no flour streaks remain in the batter.
2 cups all-purpose flour, 1½ teaspoons baking powder, 1½ teaspoons ground cinnamon, ½ teaspoon salt
Divide the muffin batter evenly between the muffin cups, each one should be nearly full.
Bake for 17-20 minutes or until the tops are puffy, rounded, and when gently touched the muffin springs back. You can also use a toothpick to test for doneness; a toothpick inserted should come out clean and with no wet, raw batter on it.
Remove the muffins from the oven and allow them to cool in the pan for about 5-10 minutes. Transfer the muffins to a wire rack to cool completely. These muffins can be eaten warm or let them cool to room temperature. Enjoy!