In large bowl, mix together the sugar, salt, and about 5 cups of flour. Dissolve yeast in warm water. Add sourdough batter & yeast & mix well. Allow the dough to rest about 20 min.
Turn onto a floured board and begin to knead, adding about 1 more cup flour, or until the dough no longer clings to the board. Knead until smooth & elastic. Put dough into an oiled bowl, turning to coat all sides. Cover & let rise until double in bulk (about 1 ½ hours).
Turn onto a floured board, divide into two pieces, knead each piece slightly, and shape into 2 loaves. Place in oiled pans. Cover & let rise. Brush tops with water and sesame seeds. Bake at 350° for 40 minutes, brushing again with water half-way through.