Prepare the Dough. Start by whisking together the dry ingredients in a large bowl – flour, baking powder, salt, and sugar.
Mix Wet Ingredients. In a separate bowl, whisk together the milk, melted butter, egg, and vanilla extract until well combined.
Combine. Pour the wet ingredients into the dry ingredients and mix until just combined. Be careful not to overmix, as this can result in a dense bite.
Shape Them. Roll the dough into small balls, about 1 inch in diameter. You should get around 12-15 bites, depending on the size.
Preheat the Air Fryer. Set your air fryer to 350°F and let it preheat for about 3 minutes.
Cook the Donut Holes. Place the donut holes in the air fryer basket, making sure they are not touching each other. Cook for 6-8 minutes, shaking the basket halfway through to ensure even cooking.
Coat Them. While they are still warm, brush them with melted butter and roll them in granulated sugar or cinnamon sugar.
Serve. Serve them warm, with a side of your favorite dipping sauce like chocolate or caramel, or enjoy them on their own!