CNN  —  Fried breakfast. Sunday lunch. Fish and chip supper. Any member of this holy triumvirate might qualify for the title of Britain’s National Dish. Except that Britain’s real signature plate isn’t served on a plate at all, but from a metalized plastic bag. It doesn’t sizzle or boil, but rustles and crunches — a greasy airbag of impetuous gratification, snacky saline satisfaction, and ultimately, empty calories. This is the story of the crisp — the wafer-thin sliced, deep-fried slivers of