In a bowl, combine sugar, 1 cup lukewarm water, yeast, then add enough flour to make dough soft, but not runny. Let stand 1 hour. To help the dough rise, put a glass filled with warm water in the center of the dough. (do not add the water to the dough yet. The glass of warm water is just to help the dough rise).
In a large bowl, measure 1 cup lukewarm water, add the dough and the salt, egg yolk, and shortening. Knead together until soft but not too soft, for ½ hour. Turn out on floured table, cover with towel. Wait about 45 minutes for dough to rise. Next put dough on a floured board and mold into a round loaf. Place in a bowl lined with a floured cloth. Let rise about ½ hour. Bake on greased cookie sheet at 350 degrees F. until done.