Preheat air fryer to 350°F (175°C) for 2-3 minutes.
In a large bowl, whisk together flour, baking powder, baking soda, salt, nutmeg, and sugar.
In a separate bowl, whisk together buttermilk, sour cream, egg, melted butter, and vanilla.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
Scoop dough into 1-inch balls (a cookie scoop works great here) and place in the air fryer basket in a single layer with space between each.
Air fry at 350°F for 6-7 minutes until golden brown.
While hot, brush with melted butter and roll in cinnamon sugar mixture.
Serve immediately.
Notes
Best eaten fresh and warm. If making ahead, store uncoated in an airtight container for up to 2 days and re-warm in the air fryer at 300°F for 2 minutes before coating and serving.