1⁄2 oz Lime juice
1⁄2 oz Agave syrup (or 2:1 simple)
1 1⁄2 oz Cola, Coca Cola
Shake, strain, rocks, top with Coke.
I haven't tried it, but the 1/2 oz of syrup may be excessive, even given the drying effects of all that Angostura.
Commenter aqaqaq at Craft Cocktails at Home
Bitters, Demerara Rum, Cola, Lime juice, Agave syrup