Activate the yeast with 1 cup cool water. Add the sugar and a little flour.
After the yeast becomes effervescent, pour it into the rest of the sifted flour. Add the oil and whites. Knead a soft dough. Leave it to double in volume.
Tear the dough into balls, roll out each one into a flat pita. Make curved cuts along it. Prepare a filling from the crumbled feta cheese and finely chopped parsley and put it on the pita.
Fold each pita and push the ends out through the holes. Smear with beaten egg yolk. Leave the dough to rise a little. Bake in a moderate oven until golden.