Put the cornmeal in a medium bowl and stir in the cold water; then add the boiling water and stir until everything is mixed together. Add in the olive oil, salt, brown sugar, caraway seeds, cocoa and instant coffee, and stir well.
Add in the yeast, stir again; then add the flours. Stir well, then begin kneading. It will be sticky at first. Knead for three to four minutes, until everything is well mixed. Form into a ball and put in an oiled bowl. Cover the bowl with plastic wrap, waxed paper or a damp towel and set in a warm place. Let it rise until double (2 to 3 hours).
Press out the air bubbles and knead for two or three minutes. Press into a rectangle about 8-1/2x11, fold it over on itself in thirds to about a 4x8 loaf, and set in an oiled 4-1/2x8-1/2-inch loaf pan. Cover and let it rise until double, about 1-1/2 to 2 hours.
Preheat oven to 375ºF. Brush the top lightly with the beaten egg white and water mix, if using (this will crisp up the crust). Bake for 25 to 30 minutes (see Kitchen Notes). Tip bread out of the pan onto a wire rack and thump the bottom to check for doneness (it will sound hollow); then let it cool.