Mix the yoghurt, sour cream and the 3 tablespoons of sugar with the whisk. Whip the cream with the vanilla sugar until stiff, fold loosely into the yoghurt mixture and divide between 2 dessert glasses.
Puree the raspberries with the hand blender and brush the mixture through a hair sieve (remove the seeds). Add sugar and raspberry brandy to taste. Pour over the dessert as a mirror. Garnish with whipped cream and raspberries.