Mix the bread flour, starter, sugar, and water in a large mixing bowl. It will seem dryer than most sourdoughs, but don't add more water. Use your hands to make sure everything is incorporated into a ball. Cover the bowl with a damp tea towel and let it rest on the counter. (It helps to measure out the salt into a separate container on place it on top of the towel so you don't forget to add it later.)
Place the dough and salt into the bread machine bucket and select the dough cycle. The machine will beep when the cycle ends, but let it rise another 2-3 hours in the machine, for a total rise time of 3-4 hours. The dough should look noticeably puffier, but may not have quite doubled in size.
Prepare a baking sheet by lining with parchment paper and sprinkling with cornmeal. Take the dough out of the bread machine, and gently shape it into a round or oval loaf. The dough will be slightly sticky, but dry not to use any flour when shaping it. Place on the prepared baking sheet and cover with plastic wrap sprayed with cooking spray.
Place the covered loaf in the refrigerator to proof overnight. Anywhere from 8-16 hours will be fine.
In the morning, preheat the oven to 450 degrees with two racks: one in the center, one in the lower middle. Place an empty rimmed baking sheet on the lower rack while the oven is preheating. Remove the loaf from the fridge and gently rub with flour. Slash the loaf with a lame or sharp serrated knife.
When the oven has preheated, pour 1 cup of water onto the empty baking sheet to create steam. Immediately place the loaf inside, close the door, and bake for 45 minutes. Let cool on a wire rack for at least 4 hours before slicing. 7. Store at room temperature, well wrapped, for up to three days,