Preheat the oven to 350°F and spray a 9x13-inch baking pan with nonstick cooking spray.

In a skillet over medium heat, brown 2 pounds ground beef until fully cooked. Drain off any excess grease.

In a large mixing bowl, stir together the cooked ground beef, 1 package (32 ounces) shredded hash brown potatoes that have been thawed, ½ chopped onion, 1 cup milk, 2 cans cream of mushroom soup, and 1 cup shredded cheddar cheese.

Pour the mixture into the prepared baking pan and spread it evenly.

Bake for 45 minutes to 1 hour until the hash browns are golden brown and tender.

Sprinkle the remaining 1 cup shredded cheddar cheese over the top and bake for 5 more minutes until the cheese is melted.

Let the casserole rest at room temperature for about 5 minutes before serving.