I have been making my roasts this way for as long as I can remember. Usually in the slow cooker, but sometimes in the oven in a covered cast iron dutch oven. It has been a family favorite for at least four generations.
I use 2 cans of soup and 2 packets of soup mix because we like lots of gravy.
Slow-Cooker Roast Beef with Mushroom and Onion soup mix gravy.
4-5 pound chuck roast
1-2 cans cream of Mushroom Soup (Last night I used one can mushroom and one can cream of celery, yum)
1-2 envelopes Onion or Onion Mushroom Soup Mix
fresh mushrooms (optional) Leave the mushrooms whole or in large chunks.
Put everything into the slow cooker, turn on high for about an hour, then reduce to low for a few hours until the meat is done to your liking. I let it go until the meat falls apart, about 5-6 hours.