Sift 2 lb (1 kg) of the flour and make a well, add the salt, yoghurt, oil and vinegar. Beat the eggs and add them.
Knead the dough for 15 min. until it becomes smooth and stretchy and doesn't stick to your hands. Cover it and leave in a warm area for 1 hour to rise and increase in volume.
Divide the dough into 3 parts. Make the 1st part the largest, the 2nd smaller and the 3rd the smallest. Shape the smallest one into a ball and put it in a tray smeared with a little butter.
Take the medium-sized part and roll it out into a thin, rectangular sheet, smear it generously with butter and wrap into a roll. Wrap it around the ball you put in the tray. Using kitchen scissors, make slight cuts along the roll, about 3/4″ (2 cm) from one another, just to open up the dough a little.
Take the largest dough part, roll it out into a sheet as well, smear with butter and wrap into a roll. Place it in the remaining space in the tray, wrapping it around the previous roll. Use scissors again to make slight cuts along the dough.
Smear the loaf with the remaining butter and leave it to rise another 30 min. Before baking, beat the egg yolk, smear the entire loaf with it, sprinkle with sesame seeds and put it in a preheated 320°F (160 °C) oven for about 1 hour to bake to a golden color.