For decades, Mortlach has remained one of Scotland’s fabled yet elusive single malts. Highly revered for its big, meaty profile, the whisky has come to be called the Beast of Dufftown, and until last year it was only available periodically in the form of limited editions from independent bottlers and occasionally the distillery itself. Much of the production was earmarked for blends, such as the Johnnie Walker Black, Platinum, and Blue Labels. But thanks to a momentous decision on the part of Diageo, the disti…