Dissolve yeast in half a cup of warm water and set aside to soften. Put flour in a large bowl, make a well in center and add eggs, oil, yeast, salt and bread spices. Mix well, adding the water a little at a time until you have a firm dough. Grease a large tray with oil. Put dough on tray and cover with a damp cloth. Place dough in a warm place for at least two hours. In a saucepan put ground beef, onion and salt. Place over medium heat, stirring until meat is cooked. Set aside until cool. Finely chop leeks and wash several times through a strainer. Spread leeks on paper towel to absorb excess water. Add leeks to ground meat. Mix sesame cream with vinegar, a little water and black pepper. When you have a smooth paste add to leek and meat mixture, mixing thoroughly. When dough has risen, roll out into circular shape of medium thickness, spread the meat mixture over the dough leaving edge uncovered. Sprinkle with poppy seeds, and place in a 350-degree oven for half an hour or until bread is baked.