In a large bowl, combine flour and water. Mix until no dry flour remains. Cover and let sit for 30-60 minutes (autolyse).
Add active sourdough starter and salt to the dough. Mix thoroughly until well combined and no streaks remain.
Perform bulk fermentation: Over the next 4-5 hours, perform 4 sets of coil folds every 30 minutes for the first 2 hours, then let rest undisturbed.
Pre-shape the dough into a round and let rest 30 minutes. Then shape into a boule or batard.
Place shaped dough seam-side up in a banneton or bowl lined with floured cloth. Cover and refrigerate 12-48 hours.
Preheat Dutch oven to 500°F for 1 hour. Score the dough and bake covered for 20 minutes, then uncovered for 20-25 minutes until golden brown.
Cool completely on a wire rack for at least 2 hours before slicing.
Notes
Storage tip: Keep cut-side down for first day, then wrap in kitchen towel. Freezes well for up to 3 months. Internal temperature should reach 205-210°F when done.