Preheat your oven to 350°F and grease a 9x13-inch baking dish.

In a large skillet over medium heat, cook the ground beef, onion, and garlic with salt and pepper until the beef is browned and the onions are translucent. Drain any excess fat.

In a large bowl, mix together the cooked beef mixture, thawed hash browns, cream of mushroom soup, milk, sour cream, and one cup of cheddar cheese until well combined.

Transfer the mixture to the prepared baking dish, spreading it out evenly.

Bake uncovered for 50 minutes, or until the edges are bubbly and the hashbrowns start to brown.

Sprinkle the remaining cup of cheddar cheese over the top and return to the oven for an additional 10 minutes, or until the cheese is melted and bubbly.

Allow the casserole to rest for 5 minutes before serving.