1. Whisk together the flours, multigrain mix, salt and yeast, evenly distributing the finer powders amongst the coarse ones. Add the warm water. Vigorously stir together the dough with the handle end of a wooden spoon, as the dough forms and until all the bottom flour is gathered up and a full dough forms. Cover and rest the dough for 12 hours.
2. Knock down the dough, sprinkle with a light dusting of any flour and form into a loose ball. Transfer it to a lightly oiled loaf pan or rest it on a baking mat as it rises again and the dough doubles in size, 1 to 2 hours.
3. Preheat your oven to 400ºF and turn on your convection fan if you have one.
4. Bake the bread until deep golden brown and crusty, 40 minutes or so. Cool, slice and share.
5. Variation: Place an oven proof pot in the oven and preheat it for 20 minutes. Turn the risen dough into the hot pot and cover with lid. Bake as usual for golden crackle crust all around.