Mix flours, salt, yeast. Add water and stir until no dry flour remains – shaggy and sticky.
Cover and ferment 12-18 hours at room temperature.
Scrape onto floured surface, fold over itself a few times, shape into ball.
Place in floured tea towel lined bowl, cover, rise 1-2 hours until puffy.
Preheat Dutch oven at 230°C for 30 mins.
Tip dough into hot pot, score, lid on.
Bake 30 mins covered, remove lid, reduce to 210°C, bake 15-20 mins until deep brown.
Cool on rack 1 hour before slicing.