Preparation - Spray a 9 "x 13" baking pan with nonstick cooking spray. Place the frozen potatoes in the pan. Sprinkle with salt and pepper. Place the melted butter, sour cream, cream of celery soup, and chopped onions in a bowl and stir the ingredients together. Pour the mixture over the potatoes. Top with the grated cheddar cheese. Bake at 350º for 45 minutes.