Mom's recipe. I used Good Season's Italian Salad Dressing mix to make marinated mushrooms. I added a bit of garlic and black pepper and a small thinly sliced onion. Simply mix the dressing, add mushrooms, simmer for ten minutes.
The dressing won't be enough liquid at first but once simmered they release enough of their own and shrink enough so they cool while covered in marinade. Quite delicious.
Refrigerate after they cool.