The "Manhattan (Bitter)" created by Chris Amirault of eGullet.org is essentially the same as this (more authoritative) cocktail by Phil Ward. Chris's version used two dashes of Angostura Orange bitters in lieu of the regular Angostura bitters, and an orange twist.
I used Jim Beam Black, because of its smoothness and full taste from being aged 8 years. I concur cardamom bitters is a nice touch. So might be black walnut bitters or Fee Bros. Whiskey Barrel-Aged Bitters. Regardless, I prefer an orange twist as opposed to orange bitters.I rate this change as 4 stars.