Mix the water and sourdough starter in a bowl. Add the flour and mix until no dry flour remains. Cover and rest for 30 minutes.
Sprinkle the salt over the dough and mix it in by squeezing and folding the dough until evenly incorporated.
Let the dough ferment at room temperature (~18 °C) for about 5–8 hours. During the first 2 hours perform 4 stretch-and-folds, spaced about 30 minutes apart.
Turn the dough onto a lightly floured surface and shape it into a tight round. Rest for 15 minutes, then shape again and place seam-side up in a floured bowl or towel-lined bowl.
Cover and refrigerate for 8–16 hours.
Place the Dutch oven in the oven and preheat to 240 °C for 45 minutes.
Turn the dough onto baking paper, score the top, and place it into the hot Dutch oven. Bake 20 minutes with the lid on at 240 °C. Remove the lid and bake another 20–25 minutes at 220–230 °C until deeply browned.
Remove the bread from the Dutch oven and cool on a wire rack for at least 1 hour before slicing.
