Spray the inside of a 6 or 8 quart slow cooker with cooking spray.
Break up the frozen shredded hasbrowns and pour into a 6 or 8 quart slow cooker.
In a separate bowl, stir together the cream of celery or onion soup, sour cream, melted butter, salt and 6 ounces of the shredded extra sharp cheddar cheese.
Add the cheese mixture to the hashbrown potatoes and stir well to combine.
Cover and cook on low setting for 2 - 3 hours, stirring once about halfway through.
Uncover and sprinkle the remaining 2 ounces of cheddar cheese on top of the casserole. Cover and cook an additional 30 minutes.
Top the casserole with fresh chopped parsley and serve.
