Comments: For the sponge, use the lower amount of water if you live in a humid climate, the higher amount in an arid climate. During kneading, this dough should not exceed a temperature of 80 degrees. If your kitchen is very warm or very cold, use water a few degrees cooler or warmer, respectively. A few pieces of equipment are highly recommended: digital scale, baking stone, parchment paper, instant-read thermometer, and spray bottle filled with water. A baking peel and razor blade are also handy but not essential. The dough can be kneaded by hand, but the kneading times must be doubled. When spritzing the loaves in the oven, be careful to avoid spraying water on the oven light.

1. MAKE THE SPONGE: In bowl or container with at least 1-quart capacity, use rubber spatula to stir together starter and water until fully combined. Stir in flour until combined; mixture should resemble thick pancake batter. Cover with plastic wrap and let rise at room temperature (about 72 degrees) until doubled in bulk, 2 to 3 hours.

2. MAKE THE DOUGH: Measure water into bowl of standing mixer; add sponge to water. Fit mixer with dough hook; with mixer running on lowest 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 with plastic wrap and let dough rest 20 minutes.

3. KNEAD THE DOUGH: Using fingers, create pocket in rested dough; add salt to pocket. Knead on low speed until dough is soft, smooth, and moist (dough should not be sticky), about 5 minutes. Transfer dough to clean work surface and knead by hand until dough forms firm ball, about 30 seconds.

4. LET THE DOUGH RISE: Lightly spray container or bowl with at least 4-quart capacity with nonstick cooking spray; place dough in container and lightly spray surface of dough. Take internal temperature of dough; then cover tightly with plastic wrap. If temperature registered 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 stand until dough doubles in bulk, 3 to 5 hours.

5. STRETCH THE DOUGH: Scrape dough out onto clean work surface. Gently stretch dough (to redistribute and refresh yeast) as far as possible without tearing, then fold it into thirds like a letter.

6. DIVIDE AND SHAPE THE DOUGH: Using bench scraper or chef's knife, divide dough in half, each piece weighing about 1 1/2 pounds. Form each half into rough ball, cover loosely with plastic wrap or damp kitchen towel, and let rest 15 minutes. To shape dough, use one hand to push dough against unfloured work surface, using other hand as guide. Goal is to make taught ball without ripping surface. Pinch bottom seam and set each round, seam side down, on separate sheets of parchment paper on dinner plates, rimless cookie sheets, or inverted rimmed baking sheets.

7. REFRIGERATE THE ROUNDS OVERNIGHT: Spray rounds lightly with nonstick cooking spray and cover loosely but completely with plastic wrap. Refrigerate overnight 8 to 12 hours.

8. PROOF AND SLASH THE ROUNDS: Remove rounds from refrigerator and gently slide onto room-temperature surface where they can rise undisturbed for several hours; space them at least 6 inches apart. Loosen plastic wrap to allow rounds to rise; let rise until at least doubled in bulk and dough barely springs back when poked with your knuckle, 3 to 4 hours. Meanwhile, after about 2 hours, adjust oven rack to lower-middle position, place baking stone on rack, and heat oven to 500 degrees. Working one at a time, carefully slide rounds on parchment onto baking peel, rimless cookie sheet, or inverted rimmed baking sheet. Using sharp razor blade or knife held at 45-degree angle to work surface, slash surface of rounds 1/2 to 3/4 inch deep.

9. BAKE THE BREAD: Working quickly, spray loaves with water, slide onto baking stone, and immediately reduce oven temperature to 450 degrees. During first 5 minutes of baking, spray loaves with water 2 additional times; bake until deep golden brown and instant-read thermometer inserted into center of loaves registers about 210 degrees, about 30 minutes total. Transfer loaves to wire rack, discard parchment, and cool loaves to room temperature on wire rack, about 2 hours.

1. Make the Sponge	2. Make the Dough
3. Knead the Dough	4. Let the Dough Rise
5. Stretch the Dough	6. Divide and Shape the Dough
7. Refrigerate the Rounds Overnight	8. Proof and Slash the Rounds
9. Bake the Bread

Begin in the evening, two days before you intend to use the starter:

1. Stir starter well to recombine, measure out 1 cup (9 ounces), and discard remaining starter (or give it to a friend). Place measured starter in glass bowl or container with at least 1 1/2-quart capacity. Stir in 1 cup (8 ounces) water until combined, then stir in 1 1/2 cups (7 1/2 ounces) flour until evenly moistened (mixture will be lumpy). Cover with lid or plastic wrap.

2. Let stand at room temperature 8 to 12 hours; repeat, pouring off all but 1 cup starter and feeding with 1 cup water and 1 1/2 cups flour, in the morning of the following day, and, finally, once again in the evening, letting it stand at room temperature for the entire time. The starter will be fully refreshed and ready to use the next morning, 8 to 12 hours after the last feeding.

Long-term starter maintenance:

To keep a starter alive over a long period of nonuse, store it in the refrigerator. It's best to feed it weekly, according to the instructions in step 1; let it stand at room temperature for 4 to 6 hours after feeding, then return it to the refrigerator.