Fill large martini glass with crushed ice and set aside. Reserve one mint sprig for garnish. Remove and discard stems from remaining mint and place leaves in a small bowl. Add sugar, and, using back of a spoon, crush mint; stir, adding a few drops of water so the sugar fully dissolves. Add small amount of ice, then the liquors. Stir to combine, and strain mixture into glass. Garnish with mint sprig.
(Recipe courtesy Barbara Smith)