Add the stew meat, red wine, onion soup mix, cream of mushroom soup, and quartered mushrooms. Stir until evenly combined and spread into an even layer.
Cover and cook on low for 10 to 13 hours, until the beef is fork-tender and the sauce is hot. Serve over noodles, rice, or mashed potatoes.
Notes
The sauce should be thick enough to coat a spoon; if it is loose, leave the lid ajar for a few minutes before serving.