All you do is take
8oz cream cheese
1/4lb crab meat
1/2 tbsp horseradish
a few splashes of Worcestershire sauce
and chopped green onions or chives to taste
Mix it up in a bowl, then stuff your mushrooms, lightly sprinkle bread crumbs ontop and bake it at 350 degrees for about 10 minutes or until you think it's done enough.
I've only ever used a real recipt once for this, and so I'm not really sure if all of my measurements up there are correct, and that's why at the end I just said "splashes, some, to taste" you know. The only part that I'm positive about is the 8oz of cream cheese. I don't have it written down anywhere either, and you could play around with the recipe to make it however you want it. I don't like really measuring things out, so I tend to just guess and taste.
Probably I should've found out what's really in this before posting, but oh well.