Add 4 tablespoons sugar, mix well, set aside. Boil briskly 6-10 minutes, gently stirring twice to loosen grains that might have stuck to bottom. In same pot, heat half remaining butter. In bowl, mix 2 spatulas of rice, the yogurt and a few drops saffron water and place mixture over butter in pot to form a crust. Repeat these steps, arranging rice in a pyramid.
Shape allows room for it to expand.
Sprinkle remaining allspice or cumin over rice. Pour remaining melted butter, saffron water and 2 tablespoons chicken juices over pyramid. Cover and cook 10 minutes over medium heat. Cook 50 minutes longer over low heat. Gently taking 1 spatula full of rice at a time, place rice on serving platter in alternating layers with barberry mixture.