Pop stems out of shrooms (don't tear cups). Cut stems up finely. Saute shrooms and onions in butter (or olive oil) slowly, over medium-low heat, until limp; be careful not to let mixture burn. Add clam juice and wine; cook slowly until most of the liquid has evaporated. Add bread crumbs to shroom mixture in pan; mix well. Should be quite dry. Add half and half until mixture has a good texture, like slightly dampish clay for hand-building pottery. Add parmesan. Fill mushroom caps with mixture (will have to mound). Bake in toaster oven at 120ºC . until mushrooms start looking shriveled and ooze juice, getting brown. If unsure, taste. Vicki's notes: Don't cut mushrooms too finely. Try adding crumbled bacon to mixture.