In a mixing bowl, whisk together the flour, 1/3 cup sugar, baking powder, salt, and 1 teaspoon of cinnamon until well combined.
In a separate bowl, mix together the milk, egg, melted butter, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. Make sure not to overmix; a few lumps are fine.
Lightly flour a clean surface and roll out the dough to about 1/2 inch thick. Using a donut cutter or two round cookie cutters (one larger and one smaller), cut out the donuts.
Preheat your air fryer to 360°F (182°C).
Place the donuts in the air fryer basket, making sure not to overcrowd (you may need to do this in batches). Lightly spray the donuts with cooking spray to help them crisp up.
Air fry the donuts for about 5-6 minutes, or until golden brown and cooked through.
In a small bowl, combine the remaining 1/4 cup granulated sugar and 1 teaspoon cinnamon.
Once the donuts are finished, remove them from the air fryer and immediately coat them in the cinnamon sugar mixture while they are warm.
Notes
Arrange the donuts on a beautiful plate, dust with a bit more cinnamon sugar, and serve with a side of warm apple sauce or your favorite dipping glaze for a delightful treat!