Sourdough - yum! Here's a version I adapted from another process. Recipes for using the starter will follow. You have to get it going first.
MASHED POTATO STARTER
3 cups thick potato water
3/4 tsp yeast
3 tsp sugar
3 cups flour
Take 4 scrubbed potatoes with jackets on, barely cover with water and boil until they fall to pieces. Lift skins out, mash the potatoes to make the 3 cups of puree. The richer the potato water, the richer the starter.
Put everything (potato puree, yeast, sugar and flour) into a sourdough pot, jar or crock (never use metal), be sure to use an extra large vessel since dough may more than triple while it's fermenting. Beat mixture until smooth and creamy. Add just enough water (if needed) to have a thick batter-like consistency. Use only wooden or plastic utensils to stir starter. Cover loosely to allow gases to escape and set aside in a warm place to start fermentation. (The inside of your microwave range hood is a good place.)
The starter can be used after only three days of fermenting; however, the longer it ferments, the better your initial product. Keep it in a warm place. At this point, some folks call this the "mother" or "sponge."
After a week, it will be effervescing with a million bubbles, will look like sour cream, have a sour smell, but it is savory, delectable sourdough. (Never add anything to the jar but sugar, flour or water). You feed the starter after you remove some for recipes.
FEED: 1 cup flour + 1 cup water +1 Tbsp sugar (if you use alot of the mother for baking then you could double up on the feeding, but don't use it for 3 - 5 days)
Even if you don't use any for baking, remove 1 to 1 1/2 cups at least once a week and feed it to keep it going. It may develop hooch (a liquid that is the by-product of the fermentation process) that rises to the top - don't worry, just stir it back in.
The longer you keep this going - the better it's flavor develops. About once a month, pour mother into another bowl (no metal) and thoroughly wash/sterilize your main jar. Pour mother back into clean jar. If at any time it looks black or a pinkish-red - flush it and start over.
Recipes using sourdough to follow.