To make the starter: Put the potatoes in a large bowl, pour the boiling water over, then stir in the cornmeal, sugar, and salt. Place the bowl in a larger bowl of hot water, and set in a warm place where the temperature remains fairly steady-a gas oven with just the pilot light on, or an electric oven with the interior light on, or on top of the water heater. Replace the hot water two or three times-or whenever you think of it and it's convenient-over the next 24 hours. Then remove the potato slices from the bowl, and continue on with the sponge.
To make the sponge: Heat the milk until it is comfortably warm to your finger, then add it to the starter, along with the baking soda and 3 1/2 cups flour. Beat briskly until smooth-a hand rotary beater helps to smooth out the lumps. Cover with plastic wrap and again place in a larger bowl of hot water. Set in a warm place (see preceding suggestions), and let the sponge double in bulk-this usually takes 2 to 3 hours, but check it after 1 1/2 hours. When doubled, it will look creamy and light. Don't let it sit longer after it is creamy and light or it will lose its "cheesy" flavor and become sour.
To make the bread dough: Put 4 cups of the flour in a large bowl. Add the salt and mix lightly with a fork. Drop in the shortening and blend it in with your fingers- as though you were making pie dough-until the mixture looks like fine meal. Add the flour mixture to the sponge and beat until well mixed. Add enough more flour-1 or 2 cups- to make a soft, manageable dough you can knead. Turn out onto a floured surface and knead for a minute or two. Let rest for 10 minutes.
Resume kneading until the dough is smooth (this dough is heavy and rather puttylike)-about 10 minutes. Divide in thirds and shape each piece into a loaf. Place in greased loaf pans. Cover with plastic wrap, set the pans in a larger pan of hot water, and again set in a warm place to rise. This final rise will take about 3 hours, and the loaves should increase in volume by about one third-this is less than the usual doubling in bulk. Bake in a preheated 350 degrees F oven for 45 to 55 minutes, until golden brown. If in doubt, better to bake a few minutes longer than underbake. Turn out of the pans and cool on a rack.
ABOUT SALT-RISING BREAD (from the Fanny Farmer Baking Book)
Salt-rising bread is something to get excited about! It was dearly loved an considered very wholesome and nutritious during the late nineteenth and early twentieth centuries, but we lost the method of making it-a result of modern technology, I think. It seems our milling process became so refined that we took the germ out of the corn kernel when milling cornmeal, and thus lost the vital nutrient needed to capture the yeast for the salt-rising bread starter. I'm happy to say the following recipe works extremely well, but you must use a nondegerminated cornmeal, such as a true stone-ground cornmeal found in health-food stores - which keeps the germ in the milling process.
The name "salt-rising bread" stems from the original method of keeping the dough warm: the bowl of dough was set in a large container of warmed rock salt, which held the heat for a long time. It's no longer necessary to keep the dough warm with salt, although it does need to be kept warmer than conventional yeast doughs-about 100 degrees F. In the recipe, I've given suggestions for convenient warm places found in almost every home.
Salt-rising bread is a great adventure to make and to eat. It is rather dense and heavy, with a creamy texture and a wonderful "cheesy" taste and aroma it will not rise quite as high as other yeast breads, but its rather compact, chewy texture makes it fabulous for toasting, and it makes the best grilled-cheese sandwiches you've ever had.