Fill a cocktail shaker two-thirds full with ice.
Pour in the light rum, fresh lime juice, orange curaçao, and orgeat syrup.
Secure the lid and shake vigorously for 15–20 seconds until well chilled.
Fill a rocks glass with fresh ice.
Strain the shaker contents into the ice-filled glass.
Slowly float the dark rum on top by pouring it over the back of a spoon just above the drink’s surface.
Garnish with a fresh mint sprig (clapped between hands to release oils) and a lime wheel.