Preheat the oven to 350 degrees Fahrenheit.
In an 8x8 casserole dish, layer the ground beef, onion, potatoes, and cheese. Sprinkle it with salt and pepper.
In a small mixing bowl, combine the cream of mushroom soup and milk. Then, pour it over the cheesy meat and potato layers.
Cover it with aluminum foil, and bake it in the oven for 1 to 1 1/2 hours or until the potatoes are fork-tender.
Remove it from the oven, and sprinkle it with French-fried onions.
Let the casserole cool for 5 minutes, and enjoy!