Mix Everything: In a large bowl, combine flour, warm water, salt, and 160g sourdough starter. Mix until everything is fully incorporated and no dry flour remains.
Bulk Fermentation: Keep the dough in a warm place if possible (75–80°F / 24–27°C). Perform 3 sets of stretch & folds at 30-minute intervals.
Shape the Dough: Lightly flour a surface and shape the dough into a boule or batard. Place in a proofing basket (or a bowl with a towel) dusted with flour.
Cold Proof Overnight: Cover and place in the fridge overnight. The dough can stay refrigerated until the afternoon, giving you the flexibility to bake it anytime the next day.
Preheat & Score: Preheat oven to 240°C (464°F) with a Dutch oven inside. Place dough on parchment paper, score the top, and load it into the hot Dutch oven.