For the Biga: Combine flour, yeast and water in large bowl of mixer fitted with dough hook. Knead on lowest speed until it forms a shaggy dough, 2 to 3 minutes. Transfer biga to a medium bowl and cover tightly with plastic wrap. Let stand at room temperature until beginning to bubble and rise, about 3 hours. Refrigerate for 8 to 24 hours.
For the Dough: Remove biga from the refrigerator and let set at room temperature while making the dough. Combine the flour, yeast and water in large bowl of mixer fitted with dough hook. Knead on lowest speed until a rough dough is formed, about 3 minutes. Turn mixer off and, without removing bowl or dough hook, cover bowl loosely with plastic wrap and let rest for 20 minutes.
Remove the plastic wrap; add the biga and salt to the bowl.(Might be easier to add the biga in pieces). Knead on lowest speed until ingredients are incorporated and the dough forms and clears the sides of the bowl, about 4 minutes. Increase mixer speed to the next setting and knead until the dough forms a ball, about 1 minute. Transfer dough to a large bowl and cover tightly with plastic wrap. Let rise in a cool, draft-free spot away from direct sunlight until slightly risen and puffy, about 1 hour.
Remove plastic wrap and turn the dough by first sliding a curved plastic bench scraper or flexible spatula underneath, then gently lifting and folding one third of dough toward center. Do the same with the opposite side of dough. Then fold the dough in half, perpendicular to the first folds. Dough should be shaped into a rough square if folded correctly. Replace plastic wrap and let dough rise 1 more hour.
Fold again as described above. Replace plastic wrap and let rise 1 more hour.
To shape the Dough: Dust work surface liberally with flour. Gently scrape the dough out of the bowl and invert onto the work surface so that the side which was on the top is now on the bottom. If you want two smaller loaves, split the dough into two equal halves. Use a knife or bench scraper. Dust the dough and hands with flour. Using minimal pressure, push the dough into a rough 8 to 10 inch square. Fold the top left corner diagonally to the middle. Repeat with the top right corner. You should now have a peak/point at the top. Gently roll the dough from the top peak/point to the bottom until it forms a rough log. Place the seam on the bottom and transfer to parchment paper. Start tucking the bottom edges underneath, working from the center to the ends, and gently stretch the dough until it is about a 16-inch long football-type shape. Dust top liberally with flour and cover loosely with plastic wrap. Let rise until doubled in size, about 1 hour.
To bake: Adjust oven rack to lower-middle position. Place baking stone on rack and preheat oven to 500°F Using a lame or a very sharp knife, cut a slit 1/2-inch deep lengthwise into the center top of the dough, starting and ending 1-1/2 inches from the ends. Using a spray bottle, spray the loaf lightly with water. Slide the parchment paper with the loaf onto a baker's peel or other large, flat surface, then onto the hot baking stone in oven. Bake for 10 minutes. Reduce oven temperature to 400° and, using the edges of the parchment paper, quickly rotate the loaf 180°. Continue to bake until a deep golden brown and an instant-read thermometer inserted into the center registers 210°, about another 35 minutes. For two smaller loaves this will be closer to 30 minutes. Transfer to a cooling rack and remove the parchment paper. Cool to room temperature before slicing.