In a small heavy bottomed saucepan, combine sugar, water and corn syrup. Bring to a boil over low heat, and set aside.

In a food processor or blender, process raspberries and their juices until smooth. Strain raspberry puree through a medium-grade mesh sieve, over a bowl, and remove the seeds. Press firmly on the solids to remove as much liquid as possible. Discard the seeds.

Return the raspberry puree to the food processor; add plums and syrup and process until smooth.

Process sorbet mixture in an ice cream maker, according to manufacturer’s instructions. Transfer sorbet to a container, cover, and freeze until set, at least 4 hours or up to 3 days. If desired, garnish with mint and berries.