Preheat the oven to 350°F (175°C).

Heat a skillet over medium-high heat. Add the ground beef and chopped onion. Cook, breaking up the beef, until no pink remains and the onion is translucent. Drain any excess fat and season lightly with salt and pepper.

Lightly grease a baking dish with oil or cooking spray. Arrange a single layer of the thin potato slices across the bottom so they overlap slightly. Season the potatoes with a pinch of salt and pepper.

Evenly spread the cooked beef and onion over the potato layer. Use the back of a spoon to smooth it into an even layer.

Dollop the cream of mushroom soup over the beef, then spread it so most of the surface is covered.

Sprinkle the shredded cheese evenly across the top. Taste and add more salt and pepper if needed.

Cover the dish tightly with foil and bake for 1 hour. Remove the foil and bake another 15 minutes until the cheese is bubbly and golden, and the potatoes are tender when pierced with a fork.