Preheat oven to 375°F (190°C) and grease a 9x13-inch baking dish.

Brown ground beef and diced onion in a skillet over medium heat. Drain excess fat and season with garlic powder, onion powder, salt, pepper, and parsley.

In a bowl, whisk together cream of mushroom soup, milk, and sour cream until smooth.

Layer half of the potatoes in the baking dish, followed by half the beef mixture, half the sauce, and half the cheese. Repeat layers.

Cover with foil and bake for 50–55 minutes. Remove foil, top with remaining cheese, and bake uncovered for 10–15 minutes until golden and bubbly.

Let rest 5–10 minutes before serving. Garnish with parsley or chives.