1. Day ahead: Wash cranberries; place on small tray. Blend in a blender and strain.
2. Several hours before serving: In pitcher or bowl, cranberry juice combine sauterne, cognac and sugar; stir until sugar is dissolved. Refrigerate.
3. To serve: Pour sauterne mixture into glass. Stir in soda.
4. Pour champagne into punch just before serving. Mix and serve.