Of course there are many different recipes and contradictory advice on the details, but the basic process begins with making an unusual starter. You boil milk or water, pour it over some cornmeal and/or wheat flour and a little salt, and let the hot mix sit in a warm place overnight until it gets bubbly and smelly from bacterial growth. Cornmeal and milk accelerate the process and help flavor the bread, but they're not essential. You mix the starter with additional flour, water, and baking soda into a batter-like sponge, and keep it warm for a few more hours until it, too, swells with bubbles. Then you add enough flour to make a dough, shape it, put it in a pan, and keep it warm for another few hours until it has doubled in volume, at which point you bake it.