Shake all ingredients with ice for 15 seconds, strain into coupe. Either no garnish, or garnish with lime twist or lime wheel.
I originally used Bacardi 1909 Superior Heritage for this, which is 89 proof. That was a limited edition release and I believe no longer available, so use another higher proof white rum (such as Diplomatico Planas) if available.
For the coffee syrup, I mixed equal parts Aeropress coffee (between a French press and espresso in strength) with demerara sugar.
Part of my 2015 "Daiquiri-palooza" of weekly daiquiri riffs for an entire year.