Mix the flour, salt and yeast in a bowl. Stir in 1 1/2 cups/375 ml water to blend. What you'll have is a wet, shaggy, sticky dough, but not so wet as to be batter. Cover the bowl with a tea towel and let it rest in a warm place for at least 12 hours, and up to 24 hours. It's ready for the next step when the surface is dotted with bubbles.
Flour a work surface and dump the dough out onto it. Sprinkle over a little more flour and fold it once or twice. Cover with the tea towel and let rest 15 minutes.
Using only enough flour to keep the dough from sticking to your fingers, shape the dough into a ball. Coat a cotton towel with cornmeal, wheat bran or flour and lay the dough on it, seam-side down. Dust with more cornmeal, wheat bran or flour. (You need quite a lot because you want to be sure the dough doesn't stick to the towel). Cover and let rise for about 2 hours. When ready, the dough will be more than double in size.
Half an hour before the dough is ready, preheat the oven to 450 degrees F/230 degrees C. Put a 2-liter cast-iron pot or Dutch oven (cocotte) inside to heat.
When the dough is ready, remove the pot from the oven and turn the dough into it, seam-side up. (It will look messy, but this is OK.) Shake the pot to settle the bread evenly. Cover with the lid and bake for 30 minutes. Remove the lid and bake until the loaf is nicely browned, another 15 to 30 minutes. Cool on a rack.