Judy - It seems to me that I've bought frozen stuffed mushrooms, but then I can't remember if I have. The first thing to go is the memory, I've been told but I can never remember what is the second thing.

I looked in my copy of "Putting Food By" by Janet Greene, Ruth Hertzberg and Beatrice Vaughan and here's what they have to say about freezing mushrooms:

"Wash carefully in cold water. Cut off ends of stems. Leave stems on fancy small buttons if you like; if mushrooms are larger than 1 inch across the caps, slice or quarter them. If serving cold (in slads, etc.), blanch in steam; if srving hot (as garnish for meats, or in combination dishes), precook.
"Blanch. In one layer, over steam--whole for 5 minutes, quarters or small caps for 3.5 minutes. (This also prevents darkening; see To Prevent Darkening early in Chapter 14.) Cool immediately; drain.
"Precooking. In table fat -- saute in a skillet until nearly done. Air-cool, or set the skillet in cold water (you'll freeze them in the good buttery juice from the pan).
"Pack. Leave 1/2 inch of headroom. Seal; freeze."

"To Prevent Darkening. Apples, apricots, peaches, nectarines, pears, and other oxidizing foods are kept from darkening by the addition of ascorbic acid (Vitamin C) either crystalline or tablets; commercial mixtures with an ascorbic acid base; crystalline citric acid; or plain lemon juice. Or steam blanching for 3 to 5 minutes, depending on size of the pieces, may be used."