Preheat your oven to 350°F.
In a large skillet over medium heat, cook the ground beef, chopped onion, and minced garlic until the beef is browned and the onion is translucent. Drain excess fat.
In a large bowl, combine the cooked beef mixture, frozen hash browns, cheddar cheese, cream of mushroom soup, milk, salt, black pepper, paprika, thyme, and sour cream. Mix well until all ingredients are evenly combined.
Transfer the mixture into a greased 9x13-inch baking dish, spreading it out evenly.
Sprinkle the mozzarella cheese on top.
Cover the dish with aluminum foil and bake for 30 minutes.
Remove the foil and bake for an additional 15-20 minutes, or until the cheese is bubbly and golden.
Let it cool for 5-10 minutes before serving.