Thaw hashbrowns slightly so they mix well. Combine hash browns, sour cream, cream of mushroom soup, cheese, milk, onion, salt, pepper, garlic salt, and 1/2 stick of melted butter. Stir… Pour into greased baking dish, and set aside. Crush croutons {easy tip: place in a ziploc bag and mash down with a rolling pin}… Spread crushed croutons evenly over the top of the casserole. Drizzle the top with other 1/2 stick of melted butter. Bake 35-45 minutes at 350 degrees.