In the mixing bowl of a stand mixer using the flat beater, combine the yeast, 2 ½ cups flour and salt. Mix on low for about 30 seconds.
With the motor running on low, pour in the warm water. Continue mixing until a shaggy dough forms. Clean off beater and switch to the dough hook. Mix in the remaining cup of flour a little at a time, to make a soft dough, adding more or less flour as needed. Knead the dough for 5 minutes. The surface should be smooth and the dough will be soft and somewhat sticky.
Turn the dough onto a kneading surface and let rest for 2 - 3 minutes while you wash and dry the bowl and spray it with non-stick spray.
Return the dough to the mixing bowl and let it rise, covered, at room temperature (about 75º) until 3 ½ times its original volume. This will probably take about 3 hours.
Gently deflate the dough and return it to the bowl. Let the dough rise at room temperature until not quite tripled in volume, about 1 ½ - 2 hours.
Meanwhile, prepare the rising surface: rub flour into canvas or linen towel placed on a baking sheet. (You can use parchment paper.)
Divide the dough into 3 pieces. Fold each piece of dough in two, cover loosely, and let the pieces relax for 5 minutes.
Shape the loaves and place them on the prepared towel or parchment. Cover the loaves loosely and let them rise at room temperature until almost triple in volume, about 1 ½ - 2 ½ hours.
Preheat oven to 450º. Set up a "simulated baker's oven" by placing a baking stone on the center rack, with a metal broiler pan on the rack beneath, at least 4 inches away from the baking stone to prevent the stone from cracking.
Transfer the risen loaves onto a peel sprinkled with cornmeal.
Slash the loaves.
Spray the loaves with water. Slide the loaves into the oven onto the preheated stone and add a cup of hot water to the broiler tray.
Bake for about 25 minutes until golden brown. (If you used parchment paper you will want to remove it after about 10-15 minutes to crisp up the bottom crust. Spray the loaves with water three times at 3-minute intervals.
Cool for 2 - 3 hours before cutting.