Step 1

Mix all ingredients. In a large mixing bowl, combine the sourdough starter, bread flour, water, sugar, and salt. You may need to use your hands or a rubber spatula to make sure all the ingredients are fully incorporated. The dough will be shaggy looking and sticky. Cover the bowl tightly with plastic wrap and allow to rest for three hours.

Step 2

Let dough rest for ten hours, stretching and folding every few hours. Cover the bowl tightly with plastic wrap and allow to rest for three hours. Stretch the dough from the outside, pulling in, to reshape the dough into a ball. Cover again and let the dough rest on the counter for three more hours. Stretch and fold again.

Step 3

Shape and cold proof overnight. Prepare a proofing basket by lining it with rice flour. Fold the dough as you have been for the stretch and folds, but this time pull it a bit tighter to form a ball. Gently place it into the proofing basket. Cover tightly with plastic wrap and allow to rest in the fridge 12 hours, or overnight.

Step 4

Remove from the fridge and score. In the morning, preheat your oven to 450 degrees with an empty Dutch oven inside. Lay out a piece of parchment on the kitchen counter, sprinkle cornmeal on it, and turn the dough out into the center. Score the loaf using a lame or serrated knife in an X shape or slash down the center.

Step 5

Bake. Carefully remove the hot Dutch oven from the oven and place the parchment with the dough inside. Place the cover on top and bake the loaf at 450 degrees for 50 minutes, with the lid on for 30 minutes and the lid off for 20 minutes. Remove from the Dutch oven, and place on a cooling rack for four hours, until fully cool.