Combine starter with water, salt, oil. Stir to loosen up the starter.
Add three cups of flour, and mix to get a thick batter.
Continue adding flour until you get a wet sticky dough.
Cover with plastic wrap or a cloth towel and let sit for 30 minutes.
Do a few stretch and folds, like maybe two on each side, then cover and let rise for about 4 hours until it has increased 75%.
Place in the refrigerator for 12-24 hours.
Divide the dough in half and form into loaves. Place on a baking pan that is covered in parchment and sprinkled with cornmeal.
Let rise 1 hour.
Preheat oven to 475°F.
Make about 3 slashes in each of your loaves, then place them in hot oven. After 15 minutes turn oven down to 425° F. and bake another 15-20 minutes. Loaves should be golden brown and sound hollow when tapped on the bottom. The internal temperature will be about 205° if using a thermometer.