Repeat the layers: another one-third of the potatoes, the remaining ground beef, another one-third of the soup mixture, and another 1/2 cup of cheese.
Finish with the last one-third of the potatoes on top, then pour the remaining mushroom soup mixture evenly over everything, making sure the top layer of potatoes is lightly coated so it doesn’t dry out.
Cover the slow cooker with the lid and cook on LOW for 6–7 hours or on HIGH for 3–4 hours, until the potatoes are very tender when pierced with a fork and the edges are bubbling.
About 20–30 minutes before serving, sprinkle the remaining 1 cup of shredded cheese evenly over the top of the casserole. Cover again and cook until the cheese is fully melted, bubbly, and just starting to turn golden around the edges.
Once done, let the casserole sit with the lid off for about 5–10 minutes to thicken slightly. Then scoop into bowls straight from the slow cooker and serve warm.
To keep this true to Nana’s 4-ingredient spirit, the base recipe only calls for ground beef, potatoes, cream of mushroom soup, and cheese, but you can still tweak it to fit your family. For picky eaters who don’t love mushroom flavor, use cream of chicken or cream of celery soup instead. If you want to sneak in veggies, scatter a handful of frozen peas, corn, or mixed vegetables between the layers without changing the main ingredients much. For a little extra flavor without adding new ingredients, season the ground beef well with salt, pepper, and any pantry spices you have on hand (garlic powder, onion powder, or paprika work nicely). You can also swap the cheddar for whatever cheese you have—American slices or mozzarella melt beautifully on top. To stretch a dollar even more, use 1 pound of beef and add one extra potato, or serve the casserole over rice or egg noodles. Leftovers reheat well in the microwave or can be turned into a next-day breakfast by topping a warmed scoop with a fried or scrambled egg.
