Preheat oven to 375°F (190°C) and grease a baking dish.
Cook ground beef in a skillet over medium heat until browned; drain excess fat and season.
Layer sliced potatoes in the baking dish.
Add a layer of cooked ground beef over the potatoes.
Add sliced onions as the next layer.
Repeat layers if needed.
Mix cream of mushroom soup with milk and pour over the layers.
Cover with foil and bake for 45 minutes.
Remove foil, add shredded cheese on top, and bake uncovered for 15–20 minutes until golden and bubbly.