1) To frost the rims of the glasses, pour a small amount of framboise into a flat dish or saucer. Place the vanilla sugar in another saucer. Briefly dip the rim of each champagne glass, 1 at a time, into the framboise and then into the sugar. Set aside to dry.
2) Pour 30ml of framboise into each glass. Add a few raspberries and then fill to just below the rim with chilled Champagne.