Gather the ingredients.
Usually, we keep our sourdough starter at 100% or higher hydration. That means when we feed it we add flour and water to make a pancake batter thick batter. To start this bread, take a half a cup or so of sourdough culture and add flour until the batter is very stiff.
Add the flour to an active culture, that is, one that has been recently fed and did not just come out of the refrigerator. Make a stiff dough.
Cover (we like to cover with plastic wrap) and leave out on the counter for 4 to 6 hours.
Use three tablespoons of the freshened, sourdough culture (or weigh out 1.3 oz.) and add the 1/2 cup water and 1 1/2 cup (total) flours in a bowl and stir until smooth. Cover this dough and keep it on the counter for about 12 hours.
The next day, add 2 3/4 c. (22.4 oz.) water, 3 c. + 2 T. (14.4 oz.) whole wheat flour and 2.5 c. - 2 T. (11 oz.) white flour to a large mixing bowl and stir until all of the flour is wet. Cover and let this dough "autolyse" for 20 minutes to one hour.
Sprinkle the salt over the dough and add the "levain" in several pieces. Mix for 2 to 3 minutes in a mixer or 5 minutes by hand. The dough is very loose. Cover.
Bulk fermentation is about 2 1/2 hours at room temperature. During this time, you will fold the dough 2 times.
To fold, turn the dough out on a well-floured board. Fold in thirds (like a letter) horizontally, then stretch the dough and fold in thirds vertically (folding step by step here).
The bread dough now weighs about 3 1/2 pounds. You may make smaller loaves out of it, but we made one large loaf for the photos.
Form the dough into a loose, round shape. Place, seam-side down, into a well-floured proofing basket or an oiled and floured bowl. Our bowl was well-floured but not oiled, and the dough stuck and deflated a bit more than I wanted.
Cover the bread loosely, without the cover touching the dough. A cardboard box would work well.
Let this dough rise 2 to 2 1/2 hours at room temperature.
About an hour before baking, preheat your oven to 440 F with a baking stone if you have it and prepare the oven for steam. (This bread can also bake without steam, when necessary.)
Sprinkle parchment paper, which is placed on the back of a cookie sheet or on a baker's peel, with flour or cornmeal or semolina. Unmold the dough from the proofing basket onto the parchment. The dough is still very wet and sticky so try your best not to deflate it.
Quickly shove the baking sheet into the oven or, using the parchment paper, move the dough onto the baking stone. Use steam for baking, as described here.
Bake for fifteen minutes, then lower the temperature to 420 F and bake until done, about 60 to 75 minutes more. Test the bread with an instant-read thermometer and make sure that it has an internal temperature of at least 195 F.
Let the bread cool for several hours on a rack. The longer the bread sits, the more intense its flavor will be. You may freeze this bread.