San Francisco sourdough bread

The tangy flavor of sourdough bread is fantastic for sandwiches.

1. In large warmed bowl, sprinkle yeast over water, stir to dissolve and let stand until bubbly. Blend in starter, sugar, salt and vinegar.
2. Gradually beat in 3 cup of the flour. Beat at least 3 minutes. Turn batter into a large oiled glass or ceramic bowl, cover with towel and let rise in warm place 1 hr or until double in bulk.
3. Combine 1 cup of the remaining flour with baking soda. Stir batter down and add flour-baking soda mixture. Gradually add remaining flour to make stiff dough.
4. Turn out onto floured board and knead, adding additional flour only as needed to prevent sticking, until dough is smooth and elastic - approximately 300 strokes of folding and turning.
5. Sprinkle a greased baking sheet with cornmeal. Form dough into 2 oblong loaves and place on sheet. Cover with towel and let rise in a warm place 1 to 1-1/2 hours, or until nearly but not quite double in size.
6. Slash the tops of loaves diagonally with a sharp razor. Mist with water and bake in 450° F oven for 10 minutes. Reduce heat to 400 and bake 35 minutes longer, or until bread tests done.
7. Remove pan of water after 15 minutes of baking. Turn out onto wire rack and cool.