With Boomsma Kloosterbitter and Carpano Antica, I...can't taste anything at ALL except vermouth. Will have to revisit this in the future. Just as a heads up.
Lovely drink. I also went more down the Dead Rabbit path, and definitely, if you use the dashes of orange bitters, it really doesn't need any sugar syrup.
I’ve been tweaking this one a bit, and lit upon the formulation known as the Dead Rabbit version: 1 1/2 oz. Irish, 1 Sweet Vermouth, 1/2 Green Chartreuse, teaspoon sugar syrup, and 2 dashes Orange Bitters. I prefer it without the syrup, but your mileage may vary. Slainte!
Couldn't help but mess with the ratios this evening (picking back up with random revisits over the past year). Settled on 50 ml - 20 ml - 15 ml. Used Clontarf and Cinzano Rosso. Could perhaps use some more tweaking, but these measures seemed to result in the best balance and expressions.