Make sourdough starter: dissolve yeast with water and add sugar until foamy. Mix in flour. Cover and let sit for 24 hours at room temperature.
After 24 hours, stir, cover again, and let stand another 24 hours.
Final baking day: stir together remaining ingredients. Mix in the sourdough starter then add the final .5 cup of warm water. Mix dough until smooth. (Add a few tablespoons of water at a time if it is too stiff.) Cover dough and let rise until doubled, 1 to 2 hours.
After the first rise, knead dough again and then shape into 1 or 2 long loaves. Place on baking sheet or pizza stone (covered), and let rise for about 1 hour, or until fully risen again.
Preheat the oven to 220 degrees C (425 degrees F). Bake for about 45 minutes. A dark crust is appropriate for this dough. Let bread completely cool before cutting.