Preheat oven to 350. Grease mini muffin pan with oil or cooking spray.
Whisk together the sour cream, egg, vanilla, oil, butter, & sugar in a bowl.
Add flour, soda, salt, & nutmeg (optional) & stir together until well combined.
Fill mini muffin pan with batter about ⅔rds full & bake for 12-16 minutes or until the sides are turning golden brown. Remove from oven & let cool in pan for 5-10 minutes then transfer to cooling rack.
For the Coating: Brush melted butter onto donut holes then either roll them around in a bowl of powdered sugar to coat or place in a ziploc bag and shake them to coat with powdered sugar.
Recipe by THE SEMISWEET SISTERS at http://www.thesemisweetsisters.com/2018/02/03/powdered-sugar-baked-donut-holes/