Gently wash the mushrooms, trimming off the stem end. Don’t soak mushrooms in water; they are like little sponges and will end up very soggy. Put the mushrooms into a slow cooker. Melt the butter and mix in the dry dressing mix. Pour over the mushrooms and stir to coat them with butter. Cover the cooker and cook on LOW for about three hours. Serve with crackers or bread to soak up the juices, if desired. This recipe will serve only about 5 people as a side dish so needs to be increased for a large potluck. Use two sticks of butter and two dressing packets for 4x the mushrooms.