Combine white rum, sherry, and fresh lime juice in a mixing glass.
Add ice and stir for 20–25 seconds until well chilled and properly diluted.
Strain into a chilled cocktail glass.
Serve ungarnished.
Sherry choice matters here - an amontillado brings hazelnut depth while a fino keeps things bone-dry and saline; avoid cream sherry, which will overwhelm the lime and throw the balance off entirely.
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