Sprinkle sugar on a plate. Moisten the rim of a champagne flute with water; hold glass upside down and dip rim into sugar.
Pour the raspberry liqueur and grapefruit juice into the glass; top with Champagne. Garnish with a grapefruit twist.
Editor’s Note: To make a batch of Mimosas (12 servings), slowly pour one bottle (750 ml) chilled champagne into a pitcher. Stir in 3 cups ruby red grapefruit juice and 3/4 cup raspberry liqueur.