Whisk flour, sugar, baking powder, baking soda, and salt in a medium bowl.
In a second bowl, whisk sour cream, milk, egg, melted butter, and vanilla.
Fold wet into dry until just combined. Rest 5 minutes.
Grease a silicone donut mold. Pipe batter into each cavity, ⅔ full.
Preheat air fryer to 325°F for 3 minutes.
Air fry at 325°F for 8 minutes, until a toothpick in the side comes out with moist crumbs.
Cool in the mold 3 minutes, then release.
Glaze or top while still slightly warm.