Dissolve the yeast in 4/5 cup (175 ml) cool water, to which you've added the sugar. Pour the flour in a suitable container, make a well and pour the effervescent yeast in it. Add the yoghurt, egg and oil and knead a soft dough. Cover it with a towel and leave in a warm area to rise until doubled in volume - about 1 hour.
In the meantime, prepare the mixture for the filling: beat 4 eggs and mix with the crumbled feta. Leave the last egg for smearing the loaf later.
Divide the dough into 4 equal parts, roll out each into a rectangle, smear each generously with pork lard. Distribute 1/4 of the filling in each and roll them up, while stretching them out a bit so they're not too thick. Cut the rolls into pieces and arrange in a pre-greased tray.
Smear with egg yolk on top and leave the loaf to rise in a warm area for about 30 min. Bake in a preheated 356°F (180 °C) oven until ready. After you take it out, sprinkle with water and cover with a towel so that the crust softens. Bon appetit!
Source: Yordanka Dimitrova.