Start by combining sour cream, dried minced onion, shredded cheese, soup, 1/4 cup of melted butter, and sea salt in a mixing bowl.
Stir the potatoes into this mixture.
Spoon the casserole into a greased 13 x 9 dish.
Combine the remaining 1/4 cup of melted butter with crushed cornflake crumbs, then top the potatoes with the mixture.
Cover the dish with foil and bake at 350 degrees for an hour, removing the foil for the last 15 minutes.
Potatoes are done when heated through and bubbling.