Mix the self-rising flour and yogurt together until shaggy, then knead in the bowl until dough is well combined and slightly sticky. The dough will be sticky, but should still be able to form into a ball and not stick to your hands too much.
Divide dough into 4 equal pieces. Roll each piece into long ropes (about 9 inches long and 1 inch in diameter.)
Spray the air fryer basket with cooking oil. Place the donuts in the air fryer, with space between them. Spray donuts lightly with cooking spray. Cook in air fryer for 7 mins at 350˚F/177˚C, flipping halfway through, until golden brown.
Let cool a few minute, then top with melted butter and cinnamon/sugar, or glaze, or other favorite donut topping (see notes for my favorite donut glaze).
Cooking time may vary depending on your air fryer. My favorite donut glaze recipe: 2 tablespoons butter, melted, 1/2 cup powdered sugar, 1/2 teaspoon vanilla, and 1/2 tablespoon hot water.
Self rising flour substitute: 1 cup all-purpose flour, 1 1/2 teaspoons baking powder and 1/2 teaspoon salt