Bring 6 cups Champagne and the sugar to a boil in a medium pan, stirring to dissolve sugar. Remove from heat; let cool. Mix remaining 6 cups Champagne and gelatin in large bowl. Let stand until softened. Stir in sugar mixture. Chill until set, at least 6 hours or overnight. Scrape gelatin with a serving spoon, and place in serving bowl; serve with whipped cream.