In a medium bowl, stir together the flours, salt and yeast. Add the water and using a wooden spoon, mix until you have a very wet, sticky dough, about 30 seconds. Add a little more water if necessary. Cover the bowl and let sit at room temperature until the surface is dotted with bubbles and the dough is more than double in size, 12 to 18 hours

When the first rise is complete, generously dust a work surface with flour. Scrape the dough out of the bowl in one piece with a spatular. Using floured hands, lift the edges of the dough in toward the centre. Nudge and tuck in the edges of the dough to make it round.

Place a tea towel on your work surface and generously dust with flour. Place dough on towel seam side down. If the dough is tacky dust with more flour and fold the tea towel loosely over the dough and let rise for about 1 to 2 hours in a draft free spot. It is ready when it has almost doubled in size. If you gently poke it and it holds the impression its ready. If not let rise a further 15 minutes

Before the end of your second rise, preheat the oven to 240 degrees C (475 degrees F), with the rack on the lower third

Unfold the tea towel and carefully place the dough into the pot seam side up. Cover and bake for 30 minutes

Remove lid and continue baking for a further 15 to 30 minutes. Its ready when it is a deep chestnut colour

Remove from oven and turn bread out on to a rack to cool throughly