In a tall glass, place:
1 t white sugar
1 sprig fresh mint
and mash the mint with a spoon to bruise the leaves and release the flavor.
1 - 2 t fresh lime juice
2 oz light rum
a splash of sparkling water
  Stir and taste.  If satisfied with the proportions, make another one for your friend.
Notes & Variations:
  1. This refreshing drink is well-known throughout Cuba, though it seems to be enjoyed more by tourists than the Cubans themselves, who tend to drink their rum straight.
  2. Use a large sprig of fresh mint, stem and all.