In a mixing bowl, combine the flour, sugar, baking powder, baking soda, and salt. Mix well to ensure that the leavening agents are evenly distributed.

In another bowl, whisk together the milk, melted butter, egg, and vanilla extract until fully combined.

Pour the wet ingredients into the dry ingredients, stirring gently until just combined. Do not over-mix; a few lumps are perfectly fine.

Dust a clean surface with flour and turn the dough out. Roll it out gently to about 1/2 inch thick. Use a donut cutter or two different-sized round cutters to cut out your donuts.

Preheat your air fryer to 350°F (175°C). Place the donuts in the air fryer basket in a single layer, making sure not to overcrowd. Air fry for about 5-6 minutes or until they are golden brown.

In a separate bowl, mix the powdered sugar, 2 tablespoons of milk, and 1/2 teaspoon of vanilla extract until smooth. Adjust milk for consistency as needed.

Once the donuts are done, let them cool for a minute or two before dipping each one into the glaze. You can add toppings like sprinkles at this stage if desired.

Allow the glaze to set for a few minutes, then serve immediately for the best flavor.