Pop cork from champagne bottle 1 to 2 hours before using. Slowly pour the champagne, allowing for foaming, into a 2-quart container; set aside.
In a medium saucepan over medium heat, combine sugar and water. Stir until mixture comes just to a boil; reduce heat to low and let simmer 5 minutes. Remove from heat, cover, and let stand approximately 10 minutes or until cool.
To the champagne, add sugar syrup, grapefruit juice, and lemon juice (do not strain pulp from juices); stir until thoroughly blended.
Ice Cream Maker - Transfer mixture to ice cream maker, process according to manufacturer's instructions.
Freezer Method - Pour into container, cover, and place mixture in the freezer. When it is semi-solid, mash it up with a fork and refreeze again. When frozen, place in a food processor or blender and process until smooth. Cover and refreeze until serving time.
Can be prepared 3 days in advance. Cover and keep frozen.
Makes 8 to 10 servings.
Champagne Grapefruit Sorbet Recipe: https://whatscookingamerica.net/SorbetChampagne.htm