Soak a brick in water overnight, then drain it and put it in the oven with the bread to create steam. This gives the loaves a firm crust.
Sprinkle yeast onto 1/4 cup warm water in bowl of electric mixer fitted with a dough hook; stir to dissolve. Let stand 5 minutes. Add remaining water, 4 cups flour and salt and beat until smooth. Beat in remaining flour 1/2 cup at a time until slightly sticky dough forms. Mix until smooth and elastic, about 8 minutes. Turn dough out onto lightly floured surface and knead until smooth and no longer sticky, adding more flour if necessary, about 3 minutes. (Dough can also be mixed and kneaded by hand. ) Grease large bowl and add dough, turning to coat surface. Cover with damp towel. Let rise at room temperature 8 hours.
Punch dough down and knead on lightly floured surface until smooth, about 2 minutes. Return to greased bowl, turning to coat entire surface. Cover with damp towel and let rise in warm draft-free area until doubled in volume, about 2 hours.
Grease baking sheets and sprinkle with cornmeal. Punchy dough down and knead on lightly floured surface until smooth, about 2 minutes. Divide into 12 pieces. Pat each into 4x7-inch rectangle. Roll up jelly roll fashion, starting at one long side. Pinch seams to seal. Arrange seam side down on prepared sheets, spacing 3 inches apart. Let rise until almost doubled in volume, about 45 minutes.
Preheat oven to 475 F. Remove brick from water and place in oven. Make 3 diagonal slashes in loaves. Brush with egg glaze. Bake 10 minutes. Reduce oven to 350 F and continue baking until loaves sound hollow when tapped on bottom, about 35 minutes. Cool on racks before serving.