1. Preheat oven to 375°F (190°C) and lightly grease a 9×13-inch baking dish.

2. In a skillet over medium heat, brown ground beef with salt, pepper, and garlic powder until cooked through; drain excess fat.

3. In a bowl, stir cream of mushroom soup with ⅓ cup milk for a smoother sauce.

4. Layer half of the potato slices in the bottom of the dish.

5. Spread half of the soup mixture over potatoes, then half of the cooked beef and half of the diced onion.

6. Sprinkle half of the cheddar cheese over the beef layer.

7. Repeat layers with remaining potatoes, soup mixture, beef, onion, and finish with remaining cheese.

8. Cover the dish with foil and bake for 45–50 minutes, until potatoes are tender.

9. Remove foil and bake an additional 10–15 minutes until cheese is golden and bubbly.

10. Let the casserole rest for 10 minutes before serving. Optionally drizzle garlic sauce on top or serve alongside.