The Anvil 100 lists the ingredients of a "The Blackthorn" as Irish whiskey, sweet vermouth, Angostura bitters, and absinthe. Now, these are the ingredients in the recipe which appears in Gary Regan's version of the "The Blackthorne" (emphasis mine) in his The Joy of Mixology book from 2003. This is the version I made - and it's terrible. Just bad - nothing good I can say about it. The whiskey and vermouth carry no weight in the cocktail, and the absinthe and bitters dominate the flavor (and not in any sort of pleasing way). So I thought "What the hell? Why would this make it on a list of supposedly unforgettable cocktails?"
Doing some research on line, I noticed that there were at least two other recipes for "The Blackthorn", neither of which has any of those ingredients in the recipe (well, one has rosso vermouth and the other has Dubonnet (an herbaceous wine-based spirit), so there is a common thread). The one I saw more often than not consisted of gin, kirsch, and Dubonnet. Unlike the first version I made, that actually SOUNDS like it would be good. So I chose to revisit this cocktail using the gin-based recipe.
The results were, as expected, the polar opposite from the first experience. This version was clean, crisp, and with just the right balance of sweet and herby so as to be complex without being "difficult." I emailed the website for the Anvil to clarify if they had mixed up the cocktail they wanted to highlight on their list. They didn't respond, so I will just give them the benefit of the doubt and assume they meant to feature the much more pleasant gin variation.
UPDATE: Recently I noted that one of the many cocktail folks I follow on Twitter, @drinkswmindy, tends bar at Anvil, so I shot her a tweet asking whether their version of this cocktail was gin or whiskey based. She was kind enough to respond that they make the whiskey version (which coincides with the List), and added they use Irish whiskey. So, that part was consistent. Turns out what I screwed up was the vermouth - I had used sweet vermouth in my original attempt based on what appeared in The Joy of Mixology by the great Gary Regan. In fact, I believe it should have been dry vermouth, per this recipe from The Wormwood Society's web site. I remade this cocktail the other day with the whiskey and dry vermouth components, and it was a huge improvement. The whiskey, dry vermouth, and absinthe all complemented each other, allowing each ingredient to play a part - the absinthe didn't dominate, which it can often do if not used in proper proportion with other ingredients. Not the best cocktail I have ever had, but it was pleasant, and was light years from the abomination I had initially created. There may be a way to make the sweet vermouth work in this, but I'll leave that to much more skilled people than me to work out.
3 dashes Angostura bitters
3 dashes absinthe (I used Lucid)
1.5oz Irish whiskey (Jameson)
1.5oz french dry vermouth
Combine ingredients in cocktail shaker with ice. Shake and strain into a chilled cocktail glass.