In a large mixing bowl dissolve yeast and 1 teaspoon of sugar in ½ cup of warm water. Cover and let stand for 5–10 minutes until it foams. Beat in 4 cups of flour and remaining ingredients, except raisins, until smooth — about 5 minutes. Add remaining flour 2 cups at a time, beating well after each addition. Add raisins. Knead with a dough hook or by hand for 10 minutes. Place in a greased bowl and turn dough to grease all over. Cover with a damp cloth and allow to rise until double in bulk — about 1½–2 hours. Punch down.Divide dough into 3 equal parts, setting a handful aside for the ladder. Roll each part into a rope 18 inches long. Taper ends. Coil rope around itself (there should be no hole in the center) and tuck ends under. Place in a round,9-inch springform pan. To make ladder, make 2 pencil- thin strips, 4 inches long, for sides; and 4 thin strips, 2 inches wide, for rungs. Fasten securely to top center of each challah. Cover and place in a warm place for 50 minutes torise again. Brush with glaze. Sprinkle with sesame or poppy seeds, if desired. Bake in a preheated 350° oven for 40–45 minutes. When challah is done, it has a hollow sound when tapped on bottom.