The Best Blueberry Muffins Ever

white sugar1 large egg1/2 cup vegetable oil1/3 cup milk1 teaspoon vanilla1 1/4 cup all-purpose flour1 teaspoon baking powder1/4 teaspoon salt1/2 cup sour cream (you can sub yogurt)1 cup blueberriesAbout 1 tablespoon white sugar for the top (optional)