1. Combine sugar and 1/2 cup water in a medium saucepan, and bring to a boil, stirring constantly until sugar is dissolved. Boil syrup 30 seconds; set aside 18 cranberries, add remaining cranberries to syrup, and cook an additional 30 seconds. Cover and remove from heat; let cranberries steep 20 minutes.
2. Strain cranberry syrup, reserving berries for another use. Transfer syrup to a glass cruet with stopper, and chill at least 1 hour. (Syrup will keep, chilled in an airtight container, up to 2 weeks.)
3. Place 3 cranberries and 1 tablespoon cranberry syrup in the bottom of each champagne glass. Top with chilled sparkling white wine, and serve immediately.
*Katherine prefers a sparkling white like Gloria Ferrer Sonoma Brut.