This cocktail is traditionally made solely with white rum, lime juice and sugar. For a twist on the classic, use Robert Lambert's Kaffir Lime Syrup instead of sugar for an extra pop of citrus.
Combine rum, lime juice and Kaffir Lime Syrup in a cocktail shaker filled with ice. Shake well, strain into chilled martini glass. Garnish with a wedge of lime or a twist of lime zest.