In a large mixing bowl combine the flour, yeast and salt. Add the water to the mix and stir until blended; the dough will be shaggy and sticky. Cover bowl with plastic wrap, and let dough rest for 18 hours at room temperature. The dough is ready when its surface is spotted with bubbles. Lightly flour a work surface and place dough on it; sprinkle it with a bit more flour to make it easier to handle, and fold it over on itself once or twice. Cover loosely with plastic wrap and let rest about 15 minutes. Using just enough flour to keep dough from sticking to work surface, gently and quickly shape dough into a ball. Coat a cotton towel with cornmeal; put dough seam side down on the towel and dust with more cornmeal. Cover with another cotton towel and let rise for about 2 hours. When it is ready, the dough will be more than double in size and will not spring back when poked with a finger. At least 30 minutes before dough is ready, heat oven to 450 degrees. Put a 6- to 8-quart heavy covered pot in the oven as it heats. When dough is more than double in size after rising for 2 hours, carefully remove hot pot from oven. Coat with non-stick spray. Slide your hand under towel and turn dough over into pot, seam side up. Shake pan once or twice if dough is unevenly distributed; it will straighten out as it bakes. Cover with lid and bake 30 minutes, then remove lid and bake another 15 to 30 minutes, until loaf is browned. Cool on a rack for at least 30 minutes before serving.