Sift the flour in a deep container. Make a well and add the sugar, vinegar, salt, oil, yeast and water (slightly warmed).
Stir well and take it out of the container. Knead on a floured counter until you get a soft dough.
Once you get a soft, elastic dough, leave it to rest in a warm area for 1 hour. Divide the dough into equal-sized balls, roll out each one thinly.
Smear each sheet with oil. Sprinkle with feta cheese and fold from all sides, in order to get a square. Toast each square on a heated saj (or pan).
Once toasted on both sides, smear it with butter. You can also use other fats (lard, oil, margarine) for smearing but with butter you're also going to get a fantastic aroma.