When there's champagne in my house, the last thing I think of is baking something with it. But this sounds so perfectly refreshing, I may yet learn some restraint. Plus, the recipe doesn't call for the entire bottle, meaning there's room for both. I found the recipe in an old Donna Hay magazine (Issue 35)
1 cup of caster (superfine) sugar
1/2 cup water
1 cup pink grapefruit juice
1 cup champagne
Place sugar and water in a saucepan over low heat and stir until dissolved. Increase to high heat and boil for one minute. Set aside to cool. Combine grapefruit juice, champagne and cooled syrup in a bowl and stir. Pour into an ice-cream maker and follow manufacturer's instructions until firm.