Special equipment: Baking stone, bench scraper, spray bottle of water, and parchment paper An instant-read thermometer and an electronic or balance scale
Place a baking stone in the middle of the oven and preheat to 470 degrees F.
Lightly dust work surface with cornmeal. With a bench scraper divide the dough into 2 equal pieces. Lightly round the halves and let rest on surface for 15 minutes.
Shape the rested dough halves into French loaves and let rest for 5 minutes. Roll each loaf into a long rope. Twist each rope into a braid. Spray the tops with water and dip the tops in sesame seeds. Transfer the shaped loaves onto the back of 2 cookie sheets lined with parchment paper, cover lightly plastic wrap. Place the loaves in a warm place and let rise for 45 to 60 minutes.
Working with 1 loaf a time, slide the scali, still on the parchment paper, onto the baking stone and and bake until crispy and brown, about 30 to 40 minutes. Transfer the scali to a rack to cool. Repeat with the remaining loaf.
In a large mixing bowl, combine the pate fermentee and water and, using your hands, break up the dough into the water.
In another bowl, whisk together the flour, yeast, and salt. Add the flour mixture to the pate fermentee mixture and mix by hand until firm and cohesive, about 3 minutes. Allow dough to rest for 10 minutes.
Turn the dough out onto a lightly floured work surface. Knead the dough until very elastic and smooth, about 10 to 15 minutes. Take the dough's temperature. It should be at 78 degrees F.
Transfer the dough to a large bowl and cover with plastic wrap (the plastic should not touch the dough). Place the bowl in a warm place (about 75 to 78 degrees F.) and let rise for a total of 1 hour and 45 minutes. After the first 45 minutes, fold the dough and turn it over in the bowl. (It will somewhat deflate the dough, but it is gentler than what's commonly referred to as "punching down.")
Let the dough rise, undisturbed, for 1 hour more. (The dough will rise considerably at this point.)
Turn the dough out onto a lightly floured work surface. Press the dough gently into a rectangle, to de-gas it.
In a large bowl, whisk together the flour, salt, and yeast. Add the water and, using your hands, mix until incorporated, about 3 minutes. (Alternatively, mix in a mixer on the lowest setting possible.) Cover bowl with plastic wrap and put in a warm place (about 75 degrees F.). Let the dough ferment for 1 hour. Take the dough's temperature. It should be at 75 degrees F.
Refrigerate the dough at least 10 hours and up to 36 hours. When ready, it will be roughly doubled in size and have a fine network of filaments and holes. Make this recipe the night before you mix the dough.
Recipe courtesy of Christy Timon & Abram Faber, Clear Flour Bread, Brookline, MA