Preparation Stir water and sugar in heavy medium saucepan over medium heat until sugar dissolves. Increase heat and bring mixture to boil.Pour mixture into medium bowl. Mix in 5 tablespoons crème de cassis. Chill mixture 2 hours. Stir Champagne into sorbet mixture. Process sorbet mixture in ice cream maker according to the manufacturer's instructions. Transfer sorbet to container; cover and freeze until firm, about 2 hours. (Can be prepared 2 days ahead: keep frozen.) Freeze 4 martini glasses or Champagne coupes for 1 hour. Scoop sorbet into frozen glasses. Garnish with small cluster of grapes, if desired, and serve. Note:If you do not have an ice cream maker, you can turn this mixture into a granita �� an Italian frozen dessert. Mix an additional 1 cup water into sorbet mixture. Freeze until semifirm, whisking occasionally, about 3 hours. Cover and freeze until solid, at least 6 hours or overnight. Using fork, scrape surface of granita to form crystals. Scoop crystals into frozen glasses; serve immediately.
Preparation Stir water and sugar in heavy medium saucepan over medium heat until sugar dissolves. Increase heat and bring mixture to boil.Pour mixture into medium bowl. Mix in 5 tablespoons crème de cassis. Chill mixture 2 hours. Stir Champagne into sorbet mixture. Process sorbet mixture in ice cream maker according to the manufacturer's instructions. Transfer sorbet to container; cover and freeze until firm, about 2 hours. (Can be prepared 2 days ahead: keep frozen.) Freeze 4 martini glasses or Champagne coupes for 1 hour. Scoop sorbet into frozen glasses. Garnish with small cluster of grapes, if desired, and serve. Note:If you do not have an ice cream maker, you can turn this mixture into a granita �� an Italian frozen dessert. Mix an additional 1 cup water into sorbet mixture. Freeze until semifirm, whisking occasionally, about 3 hours. Cover and freeze until solid, at least 6 hours or overnight. Using fork, scrape surface of granita to form crystals. Scoop crystals into frozen glasses; serve immediately.