The Cobra's Fang is one of Donn Beach's mid-period drinks — built around blackstrap rum, with passion fruit syrup and falernum providing the sweetness, and a layered cast of citrus and small accents (absinthe, Angostura, grenadine) building complexity. The drink was reconstructed by Jeff "Beachbum" Berry from Donn's surviving notes and is printed in Beachbum Berry Remixed (2010). The exact creation year is uncertain — most attributions place it in the 1940s — but the drink's structure is unmistakably Donn's.
Blackstrap rum is what bartenders reach for when they want molasses on the palate. Donn built a cocktail around it before most bars stocked it.
Blackstrap as a Base
Blackstrap rum is distilled from molasses with a high content of unrefined sugarcane character — pungent, slightly sulfurous, deep molasses notes. Cruzan Black Strap is the modern reference; Goslings Black Seal (used in Dark 'n Stormies) is in the same family but lighter. The Cobra's Fang uses blackstrap as its primary spirit, which differentiates it from the lighter rums of Donn's other drinks. The result is a cocktail with much darker color and a heavier mouthfeel — more like a long sour than a Zombie variation.
The drink's name is uncertain in origin. "Cobra" appears in several Donn Beach drink names, and the menu generally cultivated an exotic-imagined-Polynesia vocabulary that mixed actual Pacific references with invented mythology. The cocktail's name doesn't have a documented story; calling it a Donn-era stylistic choice is the honest framing.
The Spec
Two ounces of blackstrap rum, one ounce of lime juice, half ounce each of orange juice, passion fruit syrup, and falernum, with a dash of absinthe, a dash of Angostura, and a dash of grenadine. Shaken hard with ice, served tall over crushed ice.
The Three Dashes
Absinthe, Angostura, and grenadine each appear in only dash quantities, but each does specific work. Absinthe adds a faint anise top end. Angostura gives the cocktail a bittering anchor. Grenadine adds a small pomegranate sweetness that rounds the blackstrap's edge. All three are essential; substituting Pernod for absinthe is fine but skipping any of the three flattens the drink.
Blackstrap Substitutions
If you don't have blackstrap, a heavily-aged dark rum (Hamilton Black Pot, Smith & Cross) is a defensible substitute — the cocktail will read less molasses-forward but the overall shape holds. Avoid lighter Caribbean rums (Bacardi, Plantation 3 Star) here; the drink wants weight, and a lighter rum will leave it thin.
Garnish
Donn's published garnish is a mint sprig with a hibiscus or other tropical flower. Modern bars often add a lime wheel. The garnish is decorative — the drink's character is in the rum, not the trim.
Bottom Line
The Cobra's Fang is the cocktail to make when you want Donn Beach's structural approach but a heavier, darker drink than the Zombie or Three Dots and a Dash. It's also a defensible introduction to blackstrap rum if you've been intimidated by the bottle. One per evening; the molasses depth is satisfying but not session-friendly.