Ingredients
3 to 3 1/2 lb beef chuck roast, excess fat trimmed
2 large yellow onions, thinly sliced (about 6 cups)
1 (10.5 oz) can condensed cream of mushroom soup
1 (1 oz) packet dry onion soup mix
1 cup low-sodium beef broth or water
Directions
Layer the sliced onions in the bottom of a 5- to 6-quart slow cooker, spreading them out evenly. This onion bed will keep the meat off the bottom and turn into the base of your gravy.
Place the chuck roast on top of the onions. If one side is fattier, place that side facing up so the fat can baste the meat as it cooks.
In a medium bowl, whisk together the condensed cream of mushroom soup, dry onion soup mix, and beef broth or water until mostly smooth. It doesn’t need to be perfect, but you want the soup mix evenly distributed.
Pour the soup mixture evenly over the roast, making sure some of it seeps down over the sides and into the onions. Use a spoon to nudge a few onions up around the edges and on top of the meat so they’ll caramelize in the sauce.
Cover the slow cooker with the lid and cook on LOW for 8 to 10 hours, or on HIGH for 4 to 5 hours, until the beef is very tender and can be easily pulled apart with a fork. Low and slow will give you the best texture and deepest onion flavor.
Once cooked, carefully transfer the roast to a cutting board, letting the onions and gravy stay in the slow cooker. Slice the beef across the grain into thick slices or large chunks, removing any large pieces of fat as you go.
Stir the onions and gravy together in the slow cooker. The onions should be very soft and golden, and the sauce thick, glossy, and deeply brown from the slow cooking. Taste and adjust seasoning with a pinch of salt or black pepper if needed, keeping in mind the soup mix is already salty.
Return the sliced beef to the slow cooker, nestling it back into the onion gravy. Spoon the sauce over the top so every piece is well-coated. Cover and let it sit on WARM for 10 to 15 minutes so the flavors meld before serving.
To serve, lift out thick slices of beef and spoon plenty of the caramelized onion gravy over the top, making sure each portion gets a generous amount of onions and sauce.