One of the first White Castle restaurants in St. Louis MO (Maplewood) was less than a mile from our home, until we moved to the farm just before my seventh birthday.
Two bits (25 cents) got me six WC burgers, using a newspaper coupon! There was always a pile of fried chopped onions on the grill, and they covered the little square burgers with them before putting the burgers on the buns. I'm sure they used Crisco for cooking oil, or possibly lard. No Ketchup, Mustard, or other seasoning was needed. The smell was mouth watering, and I still miss them!
I've tried later White Castle burgers both fresh, and frozen, but there is no comparison to the originals.
Bill