Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish.
In a large skillet, cook the ground beef and chopped onion over medium heat until the beef is browned and the onion is translucent. Drain any excess fat.
Layer half of the sliced potatoes in the bottom of the prepared baking dish.
Spread the cooked beef and onion mixture evenly over the potatoes.
Layer the remaining sliced potatoes on top of the beef.
In a mixing bowl, combine the cream of mushroom soup, cream of celery soup, milk, salt, and pepper. Mix until well combined.
Pour the soup mixture over the potatoes in the baking dish, ensuring that it covers everything evenly.
Cover the baking dish with aluminum foil and bake in the preheated oven for 1 hour.
After 1 hour, remove the foil and sprinkle the shredded cheddar cheese evenly over the casserole.
Return the casserole to the oven and bake for an additional 15-20 minutes, or until the cheese is melted and bubbly, and the potatoes are tender.
If desired, sprinkle paprika over the top for garnish.
Remove from the oven and let it rest for a few minutes before serving.
Prep Time: 20 minutes | Cooking Time: 1 hour and 20 minutes | Total Time: Approximately 1 hour and 40 minutes
Yield: 6-8 servings