Chill 1 champagne flute that has been filled with ice cubes. Discard the ice before filling the glass with the cocktail. Squeeze the orange rind to allow its oils to rise to the surface. Rim the glass with the rind, and then drop it into the glass. Pour in the Creme de Cassis, and fill the rest of the glass 3/4 of the way with the sparkling white wine. Garnish the drink with the grapes. Cheers!