Had one of these at a bar months ago, and have been honing in on the recipe since. Here’s what we have now:
3/4 oz/shot of Falernum
2 oz/shots of Blackstrap rum (Cruzan)
3/4 tsp lime juice
3 dashes of aromatic bitters
4 ice cubes at least
(We’ve been boozing it up lately, so as not to have to move lots of mostly empty bottles.)