Sourdough San Francisco Bread

1 tb Dry yeast
1 1/2 c Warm water
1 c Sourdough starter
1 tb Sugar
1/2 tb Salt
2 tb Cider vinegar
5 1/2 c White flour
1/2 ts Baking soda
Yellow cornmeal|In lg warmed bowl, sprinkle yeast over water, stir to
dissolve and let stand until bubbly. Blend in starter,
sugar, salt and vinegar. Gradually beat in 3 c of the
flour. Beat at least 3 mins. Turn batter into a lg
oiled glass or ceramic bowl, cover with towel and let
rise in warm place 1 hr or until double in bulk.
Combine 1 c of the remaining flour with baking soda.
Stir batter down and add flour-baking soda mixture.
Gradually add remaining flour to make a stiff dough.
Turn out onto floured board and knead, adding
additional flour only as needed to prevent sticking,
approx 300 strokes of folding and turnin or until
dough is smooth and elastic. Sprinkle a greased baking
sheet with cornmeal. Form dough into 2 oblong loaves
and place on sheet. Cover with towel and let rise in
warm place 1 to 1-1/2 hr or until not quite double in
size. With sharp razor, slash the tops of loaves
diagonally. Mist with water and bake in 450 oven 10
mins. Reduce heat to 400 and bake 35 mins longer or
until bread tests done. For a harder crust, place a
pan of hot water on bottom of oven and mist with water
several times during baking. Remove pan of water after
15 mins of baking. Turn out onto wire rack and cool.
NOTE: If you like your sourdough very dar, remove the
baked bread from the pan or sheet and place under
broiler about 2 mins, or until rich brown in color.