Autolyze. Combine the bread flour, sourdough starter, sugar, and water in a large mixing bowl. The dough will feel drier than typical sourdough—this is normal. Do not add more water. Use your hands to make sure all ingredients are incorporated into a cohesive ball. Cover the bowl with a damp tea towel and let the dough rest on the counter for 30 minutes.Tip: Pre-measure the salt and place it in a small container on the towel to remind yourself to add it later. Knead. After the autolyze, transfer the dough and salt into the bread machine bucket. Then, select the “dough” cycle and press start. You don’t need to fold the dough or anything crazy like that. Just walk away.
First rise. When the cycle ends, leave the dough in the machine to continue rising for 2-3 more hours. The dough should be noticeably puffier and soft to the touch, though it may not have doubled in size. This longer rise helps develop the flavor and texture of the bread.
Shape the loaf. Prepare a baking sheet by lining it with parchment paper and sprinkling cornmeal over the surface. Carefully remove the dough from the bread machine and gently shape it into a round or oval loaf. The dough will be slightly sticky, but avoid using flour for shaping. Place the dough on the prepared baking sheet.
Second Rise (overnight proof). Spray a piece of plastic wrap with cooking spray and loosely cover the shaped dough. Place the covered loaf in the refrigerator to proof overnight for 8 to 16 hours.
Prep for baking. In the morning, preheat the oven to 450°F (230°C). Position two racks: one in the center of the oven and the other in the lower middle. Then, place an empty-rimmed baking sheet on the lower rack while the oven is preheating. Next, remove the loaf from the fridge. Dust it lightly with flour and use a lame or a sharp serrated knife to slash the top of the dough, allowing the loaf to expand during baking.
Bake with steam. When the oven is fully preheated, carefully pour 1 cup of water into the baking sheet on the lower rack to create steam. Immediately place the loaf on the center rack and close the oven door. Bake the loaf for 45 minutes until it reaches a deep golden-brown color. Remove from the oven and allow the bread to cool on a wire rack for at least 4 hours.
Slice and serve. Once the bread has fully cooled (after at least 4 hours), use a sharp, serrated knife to slice the loaf into even pieces. Enjoy fresh or toasted with your favorite toppings!