Place 70ml Armagnac (or Cognac) in a small glass bowl with a couple of prunes (look for those which come from Agen, France) and warm in the microwave. Leave to infuse for 10 minutes.

In a cocktail shaker filled with ice, pour in 35ml of the Armagnac (discarding the prunes* and saving the other 35ml for a second round),  25ml medium-dark rum, 30ml pineapple juice and some agave syrup (to taste). Shake well and strain into a chilled cocktail glass.

* Chop these up finely and add to any chocolate-based dessert for a richer flavour.