- In a saucepan, combine the grapefruit juice and sugar. Heat gently to dissolve the sugar.
- Remove from the heat.
- Pour the sweet juice in a 38 x 25-cm (15 x 10-inch) Pyrex dish. Freeze for 1 hour. Stir with a fork, scraping the sides of the dish. Return to the freezer, stirring every 30 minutes until the mixture is crumbly, about 2 hours 30 minutes to 3 hours (you should stir a total of 4 to 5 times).
- To serve, scoop the granita in the centre of 8 flared dessert cups.
- Pour about 45 ml (3 tablespoons) of sparkling wine around each scoop of granita. Serve immediately.