In a large bowl, mix starter and water until milky.
Add flour and salt. Stir until a shaggy dough forms and no dry flour remains.
Cover and rest 30–60 minutes (autolyse).
Perform 3–4 sets of stretch-and-folds every 30 minutes over 2 hours.
Cover and bulk ferment at room temperature 4–6 hours until puffy and bubbly.
Gently shape dough and place in a floured banneton or bowl.
Cover and refrigerate overnight (8–16 hours).
Preheat Dutch oven to 475°F (245°C).
Score cold dough and bake covered 20 minutes, then uncovered 20–25 minutes until deep golden.
Cool completely before slicing.