1. To make the syrup, pound the ginger and mint leaves together in a pestle and mortar until you get a paste.
  2. Stir through the lime juice and boysenberry jelly.
  3. To serve, add the syrup to a serving jug (1L approx.) along with the pineapple, whole fresh mint leaves and ice.
  4. Pour over the soda water, swizzle and serve immediately.