Heat the shmaltz or margarine in a skillet and slowly cook the onions until soft, but not brown. Add the mushrooms and cook slowly until the liquid given off by the mushrooms evaporates. Combine the hard boiled eggs and the mushroom onion mixture on a large board. Mix and chop simultaneously until the mixture is almost paste like. Season with salt and pepper. Scrape the mixture into a serving bowl, cover and chill for a few hours. Serve with crackers, toast, matzos or bread. Makes 1 1/2 cups