I put a beef roast and a pork roast into a roaster with tight cover, big enough to hold how much meat I have. (I have made up to 10 pounds of meat this way.) Pour mushroom soup over it. From one half can to two cans according to how much meat you have. Then sprinkle generously with Onion soup mix. Cover tightly with foil, put roaster cover on and cook at 250º for 12 hours.
Yes, put it into the oven before you go to bed or very early in the morning. You have the best ready-made gravy you ever tasted.