The night before baking bread, combine starter with 1 cup lukewarm water and 2 cups flour in a large bowl.
Cover tightly with plastic wrap and let stand at room temperature overnight.
The next day, dissolve the yeast in the remaining cup of water in a small bowl. Let stand for 5 minutes, stir into the sourdough mixture.
Beat in salt, olive oil and enough flour to make a soft dough.
Transfer dough to a floured board and knead, adding more flour as needed, until smooth and elastic, about 10 minutes.
Transfer to a greased bowl, cover with plastic wrap and let stand in a warm place until doubled in size (about an hour).
Punch down dough and transfer to a floured board.
Knead briefly, adding flour to keep from sticking, and shape into 2 round or oval loaves.
Dust baking sheet with cornmeal and place loaves on top.
Make a few slashes in the top of the loaves.
Cover loosely with flour-dusted dish towel and let rise in a warm place for about an hour.
Preheat oven to 450 degrees.
Bake bread for 20 minutes at 450 degrees.
Reduce temperature to 400 degrees and continue to bake another 20 minutes or until the loaves sound hollow when tapped.
Cool on a rack before slicing.