Preheat the oven to 350°F (175°C).

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 any excess fat.

In a large mixing bowl, combine the cooked beef mixture, frozen hash browns, cream of mushroom soup, milk, salt, black pepper, paprika, thyme, and sour cream. Mix well until all ingredients are evenly combined.

Transfer the mixture to a greased 9x13-inch baking dish. Spread it out evenly.

Sprinkle the shredded cheddar cheese over the top of the casserole.

Cover the dish with aluminum foil and bake for 45 minutes.

Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden brown.

Let the casserole cool for about 10 minutes before serving. Garnish with sliced green onions if desired.