KitKat
A milk-chocolate wafer first introduced in 1935 and today producing 6 million a day at the York plant (over 1 billion a year).
External Links
http://en.wikipedia.org/wiki/Kit_Kat
http://www.yorkpress.co.uk/news/8333416.Former_Rowntree_worker_recalls
_first____KitKat____bars_rolling_off_production_line_75_years_ago/
http://www.yorkpress.co.uk/news/8329865.Search_for_Rowntree_staff
_who_worked_on_the_first_KitKat_production_line/