Preheat your oven to 350°F (175°C) and lightly grease a 9×13-inch baking dish.
Place a large skillet over medium-high heat. Add the ground beef and diced onion. Cook for 6–8 minutes, breaking the meat apart as it cooks, until the beef is browned and the onions are soft. Drain any excess grease and set aside.
Layer a portion of the sliced potatoes evenly in the bottom of the prepared baking dish. Lightly season with salt and black pepper.
Add about ⅓ of the cooked beef and onion mixture over the potatoes.
Sprinkle about ⅓ of the shredded cheddar cheese over the meat layer.
Repeat the layering process two more times: potatoes, seasoning, beef mixture, and cheese. Finish with a final layer of cheese on top.
In a mixing bowl, combine the cheese soup, ½ cup milk, and the 12 oz milk. Stir until smooth. Add a pinch of salt and pepper if needed.
Pour the soup mixture evenly over the casserole, making sure it seeps down through the layers.
Cover the dish tightly with aluminum foil.
Bake in the preheated oven for 1 hour.
Remove the foil and continue baking for an additional 15 minutes, or until the top is golden and the potatoes are fork-tender.
Remove from the oven and let the casserole rest for 10 minutes before serving. This helps it set and makes slicing easier.
Serve warm and enjoy this rich, cheesy, and comforting dish.
Enjoy!
