Combine 45ml white rum, 15ml triple sec, 22ml fresh lime juice, and 10ml simple syrup in a cocktail shaker.
Add the egg white and dry shake (without ice) vigorously for 10–15 seconds to emulsify and build foam.
Add a scoop of ice and shake hard for a further 10–15 seconds until well chilled.
Double-strain into an old-fashioned glass over fresh ice cubes.
Garnish with a sprig of fresh mint and serve immediately.
Always dry shake egg white first without ice to maximize emulsification and foam volume - adding ice too early inhibits the proteins from fully binding and results in a thinner, less stable froth.
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