1. Pour the water into a large bowl and add the starter, mixing with your hands to dissolve.
2. In another bowl, whisk together the flours and salt, then add to the water-starter mixture. Using one hand, fold the flour into the mixture from the outside of the bowl inward, turning the bowl as you go and scraping down the sides as needed. Wet your hands as needed to prevent the dough sticking to your hands. Cover the mixed dough with a towel and let sit for 5 minutes.
3. Using the same outward-to-inward folding motion, knead the dough for another 5 minutes, then cover the bowl with a towel and let sit for 5 minutes. Repeat, kneading for 5 minutes.
4. The bulk rise: Cover the bowl with the towel and let sit in a warm place for 3 hours. About halfway through, knead the dough 4 times using the same folding motion. Then let sit for the remainder of the bulk rise.
5. Dump the dough onto a well-floured surface, sprinkling a little flour on top. Using both hands, grasp the sides of the dough and stretch gently into a slight rectangle. Grasp the ends and fold both toward the middle. Give the dough a quarter turn, stretch it again, and fold into the middle. Turn the dough over so that the folded edges are on the bottom, then tuck the edges underneath, gently stretching the top of the dough mound so it forms a ball. Let sit for 5 minutes.
6. Line a glass dish or bowl with a tea towel dusted with rice flour which keeps the dough from sticking better than regular flour). After resting, turn the dough over so that the folds face up. Tuck the dough inward and toward the top so that it forms a round. Turn it back over and place it in the towel-lined dish for its second rise. Let sit for 3 hours.
7. Place a 5-quart heavy Dutch oven in the oven, and preheat to 475ºF. With a sharp knife, make two or three slashes in the top of the loaf so that it expands evenly in the oven.
8. Remove the pot from the oven, open the lid, and carefully place the dough within, seam-side down. Close the lid and return the pot to the oven. The lid will trap any steam from the dough, cooking the bread all the way through and giving the loaf a crackly crust.
9. Bake for 15 minutes, covered. Remove the lid and bake for another 15-20 minutes until dark golden brown. Remove the loaf from the pot, place it directly on the oven rack, and bake another 5 minutes or so. Let cool completely on a wire rack.

Makes one 10- to 12-inch loaf.

1. Begin with 1/2 cup warm water and 1/2 cup flour. Mix well in a glass bowl, then cover with a tea towel fastened with a rubber band. Leave it out at room temperature.
2. Check on the starter after 24 hours. It should be forming bubbles and have a fermented (but not rotten!) aroma. Discard about half of the mixture, then add another 1/2 cup water and 1/2 cup flour, cover, and let sit. If it has gone bad, throw out the entire batch and start again.
3. Repeat the feeding process (discard half and add another 1/2 cup each water and flour) for about a week. Once it has a nice beerlike smell to it, it's ready to use. The starter can be stored in the refrigerator for a couple of weeks, but bring it back to room temperature overnight and feed it again before using.

Makes about two cups sourdough starter.