Preheat your oven to 350°F.
In a large skillet over medium heat, cook the ground beef, diced 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, thawed hash browns, 1 1/2 cups of cheddar cheese, cream of mushroom soup, milk, salt, black pepper, paprika, garlic powder, and onion powder. Stir until well combined.
Gently fold in the sour cream.
Transfer the mixture to a greased 9x13-inch baking dish and spread it evenly.
Sprinkle the remaining 1/2 cup of cheddar cheese on top. If using, sprinkle crushed cornflakes over the cheese for added crunch.
Bake in the preheated oven for 45-50 minutes, or until the casserole is bubbly and golden on top.
Let it cool for 5-10 minutes before serving.