Preheat your oven to 350°F (175°C). Prepare a spacious 9x13-inch baking dish.

Warm 2 tablespoons of olive oil in a large skillet over medium heat. Add chopped onion and sauté for about 5 minutes until soft.

Add 1 pound of ground beef to the skillet with the softened onions. Cook until no longer pink, around 7-10 minutes.

In a large bowl, combine cream of mushroom soup, cream of celery soup, 1 cup of milk, 1 teaspoon of salt, and ½ teaspoon of black pepper. Stir thoroughly.

Spread half of the 4 cups of thinly sliced potatoes evenly across the bottom of the baking dish.

Spoon half of the cooked ground beef mixture over the layer of sliced potatoes.

Pour half of the creamy soup mixture over the beef layer, spreading evenly with a spatula.

Layer the remaining potato slices over the top of the soup mixture, followed by the rest of the ground beef mixture.

Pour the remaining soup mixture over the entire dish, sealing in the deliciousness.

Cover the casserole dish tightly with aluminum foil and place it in the preheated oven to bake for 1 hour.

Remove the foil and sprinkle 2 cups of shredded cheddar cheese evenly on top. Bake uncovered for an additional 15-20 minutes.

Allow the casserole to cool for a few minutes before serving.