I've started using this as a basic sponge for several varieties of crusty bread, and am pleased with it.
2 cups water at room temperature
1/4 teaspoon instant yeast
(about) 3 cups strong flour
Mix until combined-the dough should not be liquid, but not dry either-more like a very wet clay. Cover, let sit at room temperature 24 hours (yes, that long).
At this point, you add salt, half a teaspoon more yeast, more water if needed, and a sweetener if you like. Add your flour (I've used both white and wheat for this) until you have a somewhat sticky dough you can handle in folds. This will be a couple cups of flour at most. Over the next two hours, fold the dough several times, taking care not to completely deflate it. After two hours, shape as desired. Let rise another hour or so until doubled slash, and bake in a hot oven with steam for the first twenty minutes (I preheat to 485 F. then drop to 425 F when I load the bread). Rotate bread pan after 20 minutes, remove steam pan if using one, and bake about 20 minutes longer until the bread has an internal temperature of around 205 degrees F. At this point, I kill the heat, pop the door of the oven open, and let the bread sit in there another five minutes directly on the rack. This helps it to release steam slowly giving the crust a crackled effect. It won't always work, but when it does, the five extra minutes is well worth it.
So that's my new basic bread sponge, and what I've been doing with it. So far, I'm sorry to say the boys prefer this to the sourdough loaves. That's a drag, as I have three lively starters at the moment.