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 250 degrees F. 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.