Sourdough Boules

Levain: On day 1 at night, mix together starter, flour, and water in a large bowl. Cover with a damp kitchen towel or a large plate and let stand at room temperature 10 to 12 hours.

Dough: On day 2 in the morning, make an autolyze: Add 525 grams (2 1/4 cups) water to levain, stirring to dissolve. Stir in flour, using a rubber scraper and then your hands to fully incorporate. (Autolyze should not feel too wet or sticky; if it does, add more flour. Err on the side of a drier dough, especially as you will be adding more water later.) Cover bowl with a damp kitchen towel; let stand at room temperature at least 30 minutes and up to 4 hours.

Dissolve salt in remaining 50 grams water (about 1/4 cup). Incorporate into dough by squeezing it in with your hands. Cover and let stand 30 minutes.

With dampened hands, grab underside of dough, stretch it out, and fold it back over itself. Rotate bowl one quarter-turn and repeat 6 more times. Cover and let stand 30 minutes. Repeat process 5 more times, letting dough stand 30 minutes between each. After final folding, dough should be soft and elastic; let rest 30 minutes more (this step should take about 3 1/2 hours total).

Turn rested dough out onto a lightly floured surface. Divide into two pieces with a bench scraper or a sharp knife. Using your hands, shape each into a loose round, rotating as you go. Let stand about 10 minutes. Meanwhile, flour 2 banneton baskets or kitchen-towel-lined bowls.

With floured hands, fold edges of dough into center to create a tighter bundle: Start by folding edge closest to you in toward center. Then fold in sides, as if creating an envelope; finally, fold top edge down. Flip dough seam-side down. Using both hands, and keeping the sides of your hands in contact with work surface, cup side of dough farthest from you and gently drag it down toward your body in a half-circle motion, simultaneously using the side of your hand to tuck edges under dough round. (This will create tension on the outside of the dough, which is necessary to maintain the shape of the finished loaf.) Continue rotating and dragging until dough is taut, smooth, and uniformly round, 3 to 4 more turns.

Use bench scraper to gently transfer shaped round to a prepared banneton or bowl, seam-side up. Repeat with second piece of dough and banneton. Cover with damp kitchen towels and refrigerate at least 8 hours and up to 1 day.

On day 3, line a 6-quart or larger Dutch oven with a square of parchment (to prevent dough from sticking to bottom) and cover with lid. Place in oven on lower rack and preheat to 500°F. Meanwhile, take dough out of refrigerator. (It does not have to return all the way to room temperature.)

Invert one dough, seam-side down, into preheated Dutch oven (or first into your hands to round it out, then into Dutch oven). Use a bread lame, razor, or knife to score top of loaf. Drop a couple of ice cubes on top (optional), cover, and bake 20 minutes. Reduce temperature to 450°F; bake 10 minutes. Remove lid and bake until crust is dark golden brown and boule sounds hollow when tapped, 15 to 25 minutes more.

Remove from oven; transfer loaf to a wire rack and let cool completely. Let Dutch oven cool 10 minutes before cleaning it out and repeating entire process with second loaf. (If you have two Dutch ovens, you can bake both loaves at the same time.) Cooled loaves last about 2 to 3 days, well-wrapped at room temperature. Or cut them into quarters or slice, place in freezer bags, and freeze up to 1 month.