Preheat oven to 375°F (190°C).
In a skillet, cook ground beef and chopped onion over medium heat until beef is browned and onions are softened. Drain excess fat. Season with salt and pepper.
In a greased baking dish, layer half of the sliced potatoes. Top with half of the beef mixture, half of the shredded cheese, and half of the mushroom soup.
Repeat layers with remaining potatoes, beef, cheese, and soup.
Cover with foil and bake for 45 minutes. Remove foil and bake an additional 15–20 minutes, until potatoes are tender and cheese is golden and bubbly.
Let stand for 5–10 minutes before serving. Garnish with fresh parsley if desired.
Serving and Storage Tips:
