Fill a large bowl with ice and water; set aside. Bring a medium pot of water to a boil. Add plums; blanch until skin begins to peel, 2 to 3 minutes. Remove plums from water; place in the ice bath until cool. Remove plums from ice bath, reserving ice bath.
Peel plums, remove pits, cut into chunks, and place in a medium saucepan. Add the raspberries, wine, sugar, tarragon, triple sec (if using), and the water to the saucepan; cover, and bring to a simmer over medium heat. Reduce heat to medium low, and allow to simmer until plums are falling apart, 15 to 20 minutes. Remove from heat, transfer to a clean bowl, and place in the reserved ice bath, stirring occasionally, until cold.
Remove tarragon sprigs from cold mixture, and transfer mixture to a blender. Puree, working in batches if necessary. Serve garnished with diced plum, raspberries, and tarragon.