In a medium mixing bowl, thoroughly whisk together the flour, granulated sugar, baking powder, baking soda, and salt until the mixture is evenly blended.
In another bowl, combine the buttermilk, egg, melted butter, and vanilla extract. Whisk until the mixture is smooth and well incorporated.
Slowly pour the wet ingredients into the bowl with the dry ingredients, stirring gently until just combined. Be careful not to overmix; it's acceptable for the batter to have a few small lumps.
Preheat your air fryer to 350°F (175°C) for about 5 minutes to ensure even cooking.
Using a small cookie scoop or your hands, portion out the dough into small balls, each about 1 inch in diameter. Place them on a parchment-lined tray for easy transfer.
Lightly spray the air fryer basket with cooking spray to prevent sticking. Arrange the donut holes in a single layer in the basket, ensuring they do not touch each other for optimal air circulation.
Air fry the donut holes for about 5-6 minutes, or until they are golden brown and fully cooked through.
As soon as they come out of the air fryer, toss the warm donut holes in powdered sugar or cinnamon sugar in a large bowl until they are evenly coated.
Let the donut holes cool slightly on a wire rack before serving; they are best enjoyed warm!
Notes
Best enjoyed warm. Can substitute buttermilk with milk and lemon juice.