Combine cornmeal and boiling water in a large glass measuring cup. Add molasses and let stand for 5 minutes or longer to soften the cornmeal and to cool the liquid until it is the temperature of a baby's bottle (105 to 115°F).
Combine whole-wheat flour, bread (or all-purpose) flour, yeast and salt in a food processor. Pulse to mix. With the motor running, gradually pour the cornmeal mixture through the feed tube until a ball forms. Process for about 45 seconds to "knead" the dough (it will be sticky). Turn the dough out onto a floured surface. Cover with plastic wrap and let rest for 10 minutes.
Coat a baking sheet with cooking spray. Dust with cornmeal (or flour), shaking off excess. Punch down dough and form into a 7-inch-diameter round loaf. Place on the prepared baking sheet. Cover lightly with plastic wrap that has been coated with cooking spray and let rise until doubled in bulk, 40 to 45 minutes.
Set a rack in the center of the oven; preheat to 425°F. Just before baking, place a shallow pan of hot water on the lowest shelf in the oven.
Brush the risen loaf lightly with the egg-white mixture, taking care not to let it drip onto the pan. Use a sharp knife to make two slashes, 1/2 inch deep, in a crisscross pattern on top.
Bake the bread for 10 minutes. Brush again with the glaze and rotate pan 180° (from front to back). Lower oven temperature to 400° and bake for 10 to 15 minutes more, or until golden and the bottom sounds hollow when tapped. Transfer the bread to a wire rack to cool.