Preheat the oven to 350°F. Line a 12-cup muffin pan with parchment paper muffin liners, and then lightly spray each muffin liner with cooking spray. Set aside.
In a large mixing bowl, whisk together the granulated sugar, light brown sugar, vegetable oil, and large egg until it's well combined.
1/3 cup granulated sugar, 1/3 cup packed light brown sugar, 1/3 cup vegetable oil, 1 large egg
Add the cinnamon applesauce, sour cream, whole milk, and vanilla extract. Continue whisking until combined.
1 cup cinnamon applesauce, 1/4 cup sour cream, 2 tablespoons whole milk, 1 teaspoon vanilla extract
Add in the dry ingredients; all-purpose flour, baking powder, cinnamon, and salt. Stir with a wooden spoon or rubber spatula just until combined and no flour streaks remain in the batter.
2 cups all-purpose flour, 1½ teaspoons baking powder, 1 teaspoon ground cinnamon, ½ teaspoon sea salt
Scoop the muffin batter into each muffin cup filling each one nearly to the top.
Bake for 16-20 minutes or until the tops of the muffins are puffy, rounded, and when gently pressed it springs back. You can also use toothpick to test the centers of the muffins. It should come out clean or with crumbs, not wet raw batter.
Remove the muffins from the oven and allow them to cool inside the warm muffin pan for about 15 minutes or until you can safely handle them.