In a large bowl, mix the water and starter, then stir in the flours until no dry spots remain. Cover and autolyse for 1 hour.

Sprinkle the salt and a splash of water over the dough, then fold 4 to 5 times with a wet hand until tension builds.

Cover and rest 30 minutes, then perform a coil fold. Repeat two more sets of folds at 30-minute intervals, then cover tightly and let the dough rise at room temperature for 7 to 12 hours until nearly doubled.

Turn the dough onto a floured surface, shape into a tight round, and place seam side up in a floured banneton. Proof for 1 to 2 hours until a poke springs back slowly.

Preheat a Dutch oven at 450°F (230°C) for 30 minutes. Invert the loaf onto parchment, score the top, and bake covered for 25 minutes. Uncover and bake 20 to 25 minutes more, then cool on a rack for at least 2 hours before slicing.