Make the Dough:
In a large mixing bowl, combine the self-raising flour and yogurt. Stir until a soft dough forms. Transfer the dough onto a lightly floured surface and knead gently with your hands until smooth, ensuring there are no dry patches of flour. If the dough feels sticky, rub a little oil on your hands to help manage the dough without sticking.

Shape the Donuts:
Divide the dough into two portions and roll each portion into a long log, about 1-inch thick. Using a dough scraper or knife, cut the dough into small pieces, roughly weighing 8–12 g each. Gently roll each piece between your palms to form smooth doughnut balls.

Air Fry the Donuts:
Preheat your air fryer to 350°F (180°C) for about 5 minutes. Lightly brush the air fryer basket with oil to prevent sticking. Toss the doughnuts in melted butter and place them in the basket, leaving space between each doughnut as they will expand while cooking. Air fry for 5 minutes, or until puffed and golden (note: they may not brown evenly, which is normal for air frying).

Finish with Cinnamon Sugar:
While the doughnuts are still warm, coat them in melted butter, then immediately roll them in the cinnamon-sugar mixture to ensure the sugar sticks perfectly.

Serve:
Enjoy these light and fluffy doughnuts as they are, or dip them in melted chocolate for an extra indulgent treat!