1. Preheat the oven to 350°F.
2. Heat a large skillet over medium heat and brown 2 pounds of ground beef, breaking it into crumbles with a spatula. Drain any excess grease.
3. Peel and thinly slice or cube Russet potatoes to ensure even cooking; set aside the prepared potatoes.
4. In a mixing bowl, combine 2 cans of cream of mushroom soup with 1 1/2 to 3/4 cups of milk. Stir until smooth and fully blended.
5. Add diced onions, minced garlic, Worcestershire sauce, and seasonings like salt, pepper, thyme, or Italian seasoning to the soup mixture and mix thoroughly.
6. In a 9×13 baking dish, begin the layering process with a layer of thinly sliced potatoes, followed by half of the browned ground beef.
7. Pour half of the soup mixture evenly over the ground beef, then sprinkle half of the cheese on top.
8. Repeat with another layer of potatoes, the remaining ground beef, the rest of the soup mixture, and the remaining cheese on top.
9. Cover the baking dish with aluminum foil and bake in the preheated oven for 45 to 90 minutes, checking every 15-20 minutes.
10. Test the casserole by inserting a fork to ensure the potatoes are tender.
11. Once the potatoes are fork tender, remove the foil and bake for an additional 10-15 minutes to achieve a golden, bubbly cheese top layer.
12. Let the casserole cool slightly before serving for the best texture and flavor.