In a cocktail shaker half full of ice, combine the white rum, orange curaçao, lime juice and orgeat. Cover and shake vigorously for 10 to 20 seconds.
Strain the cocktail into a rocks glass three-quarters full of ice. Float the dark rum over top (see notes).
Garnish with a lime wheel, cherry and mint sprig, if desired.
Notes
To properly “float” the dark rum on top of the cocktail, hold the rounded side of a cocktail spoon facing up over the top of the cocktail. Slowly pour the dark rum over the rounded spoon. It should slowly pour over all sides of the spoon and stay on top of the cocktail.