"This is a very old recipe made often on the prairie by the pioneers who could not buy yeast at a store, so they had to make their own. It is a very easy recipe, but it does take a little extra time for the rising. So if you are in a hurry, this is not the recipe for you. It has a taste like sourdough and is a favorite in my family. Perfect for sandwiches!"
Combine potatoes, cornmeal, 1 teaspoon salt, and sugar in a large bowl. Pour boiling water on top. Cover with a dish towel; let sit for 24 hours in a warm place.
Remove potatoes from the yeast water, and add milk, 1 cup water, butter, 1/8 teaspoon salt, and baking soda to the bowl. Add 1 cup flour at a time, stirring constantly, until dough begins to come together and pull away from the sides of the bowl.
Turn dough out onto a floured surface; cut into 3 equal pieces. Knead each piece until soft and elastic. Place dough in 3 well-buttered bread pans and turn to coat. Cover loosely with greased plastic wrap and let rise in a warm place until doubled in size, about 24 hours.
Preheat an oven to 400 degrees F (200 degrees C).
Bake in the preheated oven until tops are golden brown, about 45 minutes.