Add all the dry ingredients to a large bowl and mix well to combine. Add the water and stir until shaggy.
Cover with plastic wrap and let the dough rise at room temperature for 8-9 hours, then in the fridge overnight. In the morning let it come back to room temp and finish bulk fermenting (about 4 hours).
Turn the dough over onto a lightly floured surface and shape. Transfer to a banneton and let it rise for 1-2 hours.
Preheat the oven to 240C. Score and load the bread into the oven, bake with steam for 15 minutes, then a further 15-20 minutes at 220C.
