24-Hour Sourdough Bread

1. FOR THE SPONGE: Stir starter and water together in large bowl until fully combined. Stir in flour until combined (mixture should resemble thick pancake batter). Cover bowl tightly with plastic wrap and let rise at room temperature until doubled in size, 2 to 3 hours.
2. FOR THE DOUGH: Add water and sponge to bowl of stand mixer fitted with dough hook. With mixer on low speed, add flour, 1⁄2 cup at a time. Once all flour has been added, continue kneading until dough forms ball, about 1 minute longer; cover bowl tightly with plastic, and let dough rest for 20 minutes.
3. Using fingers, create pocket in rested dough, then add salt to pocket. Knead dough on low speed until soft, smooth, and moist (dough should not be sticky), about 5 minutes. Transfer dough to clean counter and knead by hand to form firm ball, about 30 seconds. Place dough in large, lightly greased bowl, and spray surface of dough lightly with vegetable oil spray. Take internal temperature of dough; then cover tightly with plastic. If temperature is below 78 degrees, set container at room temperature (about 70 degrees) in draft-free spot; if warmer than 78 degrees, set container at cool room temperature (about 65 degrees) in draft-free spot. Let rise until dough doubles in size, 3 to 5 hours.
4. Line 2 rimmed baking sheets with parchment paper. Transfer dough to clean counter. Gently stretch dough (to redistribute and refresh yeast) as far as possible without tearing, then fold it into thirds like business letter. Divide dough in half crosswise, then loosely shape each piece into ball, cover loosely with plastic, and let rest for 15 minutes. Cup hands stiffly around 1 piece of dough (keep other piece covered), and drag in short half-circular motions toward edge of counter, forming dough into round loaf with smooth, taut surface. Pinch bottom seam closed and set loaf seam side down on prepared baking sheet. Repeat with second piece of dough. Spray loaves lightly with oil spray, cover loosely with plastic, and refrigerate for at least 8 hours or up to 24 hours.
5. Slide parchment and covered loaves onto clean counter, spaced at least 6 inches apart. Loosen plastic to allow loaves to rise; let rise until nearly doubled in size, 3 to 4 hours. (Dough should barely spring back when poked with knuckle.)
6. One hour before baking, adjust oven rack to lower-middle position, place baking stone on rack, and heat oven to 500 degrees. Carefully slide parchment and rounds onto pizza peel. Using sharp serrated knife or single-edge razor blade, held at 45-degree angle to work surface, slash surface of loaves 1⁄2 to 3⁄4 inch deep. Working quickly, spray loaves with water, slide parchment with loaves onto baking stone, and immediately reduce oven temperature to 450 degrees. Bake, spraying loaves with water twice more during first 5 minutes of baking, until crust is deep golden brown and loaves register 210 degrees, about 30 minutes. Transfer loaves to wire rack, discard parchment, and let cool to room temperature, about 2 hours, before slicing and serving. (Bread can be wrapped in double layer of plastic wrap and stored at room temperature for up to 3 days. Wrapped with additional layer of aluminum foil, bread can be frozen for up to 1 month.)

SOURDOUGH STARTER REFRESHMENT
If you do not already have a starter, dried starter packets (sold by mail and in some natural foods stores) or fresh mail-order starters work well. Follow the package directions to get the starter going, then follow our directions for feeding once the starter is going strong. No matter where you get your starter and how carefully you maintain it, you should refresh it according to the instructions below before using it.
3 cups water, heated to 80 degrees
4-1⁄2 cups (22-1⁄2 ounces) all-purpose flour

1. Beginning in evening, 2 days before you intend to use starter, stir starter well to recombine. Measure out and reserve 1 cup (9 ounces) of starter; discard remaining starter (or give it to a friend). Stir reserved starter and 1 cup water together in large bowl until combined, then stir in 1-1⁄2 cups flour until evenly moistened (mixture will be lumpy). Cover with plastic wrap and let mixture stand at room temperature for 8 hours to 12 hours.
2. In morning of following day, pour off all but 1 cup starter, stir in 1 cup water, then stir in 1-1⁄2 cups flour. Repeat with pouring off starter, stirring in remaining 1 cup water and remaining 1-1⁄2 cups flour, letting it stand at room temperature for entire time. Starter will be fully refreshed and ready to use next morning, 8 to 12 hours after last feeding. (Starter can be kept alive over long period of nonuse in refrigerator. It’s best to feed it weekly, according to instructions in step 1; let it stand at room temperature for 4 to 6 hours after feeding, then return it to refrigerator.)