Mix the mascarpone, yoghurt, sugar and vanilla sugar together, then fold in the frozen raspberries. Wrap the cantuccini in a kitchen towel and pound it. Put half of the cantuccini pieces in 4 whiskey glasses, then half of the mascarpone cream, then another layer of cantuccini and the rest of the cream. Place the glasses in the refrigerator for at least 1, preferably 2 hours, and let them steep. Garnish with whipped cream to serve.