The Widow's Kiss is a fairly old cocktail, dating back to around 1895. This was during a time when a "new" age of cocktails were coming into existence as bartenders were letting it expand beyond its previously held definition of "spirits of any kind, sugar, water, and bitters". They were experimenting with the use of vermouth (and hence the Martini and Manhattan), as well as various herbal liqueurs which would have previously been simply sipped neat. The Window's Kiss doubles up on its elixir content by using both Chartreuse and Benedictine. If you can only find green Chartreuse and not yellow, you can substitute it if you cut back on it by about a third.