I found this recipe in one of my grandmother's cookbooks, which is at least 50 years old. The recipe states that it's "an old recipe handed down in the family" (not mine). I tried this recipe once, but found the sourdough taste more pronounced than I care for. The loaves had a lovely, even crumb.
Cook potatoes with peelings. Peel while hot and mash or put through a ricer. To 5 cups mashed potatoes stir in as much rye flour as you can. Set this in a warm place for 2 days. Stir a few times. It will get thinner as it ferments. To this mixture add:
1 quart buttermilk
1 cup water
1 cup molasses
3/4 cup shortening
1/2 cup sugar
1/4 cup salt
1-1/2 teaspoon crushed fennel seed
3 yeast packages
(More rye flour and white flour, to be added during kneading)
Have all this lukewarm. Let this rise until light. Knead using about 2 cups more rye flour, rest white flour. Do not knead it too hard. Let rise and knead down again. After second rising form in eight small loaves. Let rise until about double in size. Bake at 350 for 1 hour. Brush top of loaves with molasses water a couple times during baking. This bread is heavy so it will rise much slower than ordinary bread.