I know it sounds weird to put cranberry sauce with a roast, but once it’s done cooking it is so good. And it couldn’t be easier!
Place onion soup mix in the bottom of a slow cooker. Place roast in the slow cooker, and top with cranberry sauce.
Cover, and cook 8 hours on Low.
Remove roast, and set aside. Set slow cooker to High. Whisk together butter and flour, and slowly mix into the liquid remaining in the slow cooker to create a thick gravy. Serve with the roast.