Dissolve yeast and sugar in warm water in a large bowl; let stand 5 minutes. Lightly spoon flour into dry measuring cups, and level with a knife.
Add 5 3/4 cups flour and salt, and beat with a mixer at medium speed until smooth. Turn dough out onto a floured surface. Knead until smooth and elastic (about 10 minutes); add enough of remaining flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel tacky).
Place the dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85), free from drafts, for 45 minutes or until doubled in size. (Press two fingers into the dough. If an indentation remains, the dough has risen enough.) Punch dough down; cover and let rest for 5 minutes. Divide in half. Working with one portion at a time (cover remaining dough to keep from drying), shape each portion into a 12-inch loaf on a floured surface.
Place the loaves on a large baking sheet coated with cooking spray and sprinkled with cornmeal. Cover and let rise for 15 minutes.
Uncover dough.
Brush the loaves with cold water; make 5 diagonal cuts 1/4 inch deep across top of each loaf using a sharp knife.
Place baking sheet in cold oven, and set to 40
Bake 40 minutes or until loaves are browned on bottom and sound hollow when tapped.
