The day before; mix starter, water, and 3 cups of the flour(362 gm). Cover with a damp towel, and let this sponge sit at room temperature for 2 hours; then refrigerate overnight, or for up to 16 hours.
The next day: add the yeast, salt, oil, and enough of the remaining 2 1/2 cups flour to make a soft dough that cleans the sides of the bowl. Turn the dough out onto a lightly floured or oiled work surface, snd knead it for at least 10 minutes, adding more flour as necessary, until it is smooth and springs back when you poke it. If the dough feels too stiff, add a few more teaspoons of water to soften it.
Place the dough in a lightly greased bowl, cover it with lightly greased plastic wrap, and let it rise for 2 hours at moderate room temperature (below 80F or so). The dough should become puffy.
Press the dough down and divide it into two pieces. Form each piece into a round ball, and place each ball on a baking sheet that has been greased and sprinkled with cornmeal. Cove the loaves with damp towels or lightly greased plastic wrap, and allow them to rise fr 1 hour or longer until they've become puffy and a pressed finger leaves a mark.
While loaves are rising, preheat the oven to 425F.
Bake for about 25 to 30 minutes, until the bread is golden, sounds hollow when tapped, and internal temperature is 190F to 205F on a digital thermometer.
Remove bread from the oven and cool completely on a rack.
Store loosely wrapped for 3 days, or wrap tightly and freeze for up to 3 months.