Preparation

Preparing the dough

• Begin by preparing the rye starter and the wheat starter. Both must rest, covered at room temperature, for 12 to 20 hours; the rye starter will have the texture of very soft clay.
• Portion the starters by weight—7-1/2 ounces of the rye and 5 ounces of the wheat. Put the weighed starters in a medium bowl. In a large bowl, mix the flour and salt. Dissolve the yeast in the water in a measuring cup, add that to the starters, and use your hands to combine well. Add the starters to the flour and salt, and mix by hand until the mixture comes together in a sticky, shaggy mass.

Kneading and rising

• Turn the dough out onto a clean surface that has not been floured. Knead by pushing the dough away from you, folding it back toward you, turning it a quarter turn, and pushing it away from you again. The dough will be very sticky, but resist the urge to add flour; instead, use a pastry scraper to bring up any dough that sticks. Continue kneading for about 8 minutes. To get the smoothest, best-developed dough, let it rest for about 10 minutes, covered with a damp towel, and then resume kneading for another few minutes. The dough has been sufficiently kneaded if it springs back when you poke it with your finger.
• Put the dough in a large, lightly oiled bowl and cover with a damp cloth. Let it rise in a warm (but not hot), draft-free area until not quite doubled, about 1 hour. When the dough reaches this size, gently deflate it and give it a quick knead or two. Return the dough to the bowl and let it rest another 1/2 hour.
• Now cut the dough in half and gently flatten each piece into a disk. Fold an edge up, overlapping the disk by two-thirds. Rotate the disk slightly and fold again; repeat, overlapping the folds (there will be about five) until you reach the original fold. As you fold, gently stretch the underside of the disk. Roll the dough over so the smooth side is up.
• Stretch the surface taut by gently pressing the dough against the work surface with cupped hands, tucking any excess dough underneath. Take care not to rip the surface. Cover the balls with a damp cloth and let them rest for 15 to 20 minutes.

Forming the loaves

• Set the dough balls, seam side up, on a lightly floured surface. Flatten one ball into a rectangle about 7 inches across and 8-1/2 inches long. Fold the top toward you about two-thirds of the way down and press the dough with the heel of your palms to seal. Pick the dough up and turn it around 180 degrees; the fold will be nearest you and the single edge farthest from you. Fold the top toward you to about two-thirds of the way down (like a business letter) and press the seam again to seal. Now fold the dough again, this time in half, bringing the top edge all the way to the bottom edge. Seal the edge with the heel of your hand, flattening the tight cylinder somewhat. Roll the somewhat flattened dough into a cyllinder about 11 inches long, tucking in the ends and pinching them lightly. Repeat with the other ball of dough.
• Put the loaves on the back of a well-floured baking sheet or pizza peel. Cover with a damp cloth and let rise in a warm, draft-free area until almost doubled, about 45 minutes.

Baking

• While the loaves rise, get your oven ready: put a baking stone on the middle shelf and a heavy, ovenproof, rimmed pan on the bottom shelf or oven floor, and set the oven for 450ºF.
• Slash the tops of the risen loaves perpendicularly with a razor blade, making 4 or 5 shallow cuts. Carrefully pour a small amount of water into the hot pan in the oven and quickly close the door to create some steam.
• Place the baking sheet or the peel on top of the stone and quickly pull it away from under the loaves so that they drop onto the stone. Spray the loaves with water from a spray bottle and add a little more water to the pan. Bake the bread for 10 minutes. Reduce the oven temperature to 400ºF and bake for another 10 minutes. Rotate the loaves and bake until they’re an even brown color and have a slightly hollow sound when tapped on the bottom, another 15 to 18 minutes.
• Cool the bread on a wire rack. For the best flavor, don’t slice the bread until it has cooled almost completely.

Make Ahead Tips

The leftover starters will keep for up to a week in the refrigerator.