Build in a Collins glass filled with fresh ice. Add ginger beer first, then lime juice if using. Float the dark rum on top by pouring slowly over the back of a barspoon. Garnish with a lime wedge.
Bermuda, post-WWI. Gosling's owns the trademark and has sued bars; technically only Gosling's makes a "Dark and Stormy." We use the spirit of the drink with house dark rum.
Collins glass, fresh ice, the dark rum visibly floating on top — that's the "storm cloud." Stir to integrate or sip the layers.
Spicy, warming, refreshing. The float visual is part of the experience.