The Diamondback referred to is the Maryland terrapin, which makes sense given this herbaceous cocktail originated in Baltimore's Diamondback Lounge.
The original recipe and others I've read don't include the bitters, but I'm going to suggest you give that a try. If it's not to your liking, leave it out.
Thanks to Cold Glass for the take on this cocktail.
Place all the components in a mixing glass with ice and stir until chilled. Server up in a coupe.
Photos by Lisa Denkinger
Off to Osaka Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0 License http://creativecommons.org/licenses/by/3.0/