In a large saucepan over medium heat, cook wine until reduced by half, about 30 minutes. In a small bowl, stir sugar and cornstarch; add to wine, and whisk to dissolve. Simmer until slightly thickened, about 3 minutes. Add rhubarb, and remove from heat.Advertisement
Tie mint and lemongrass together with kitchen twine; add to rhubarb mixture. Cover and chill 2 hours, or overnight.
To serve, remove herb bundle. Ladle cold soup into bowls; place a scoop of cheese sorbet in center of each.