Soak gelatine in cold water. Mix yoghurt, nectar and sugar. Squeeze the gelatine well and dissolve in a pot at low heat. Add some of the yoghurt/passion fruit mixture and mix. Then stir into the rest of the yoghurt mixture and chill. Whip cream and vanilla sugar until stiff.
When the yoghurt mass begins to gel, fold in the cream. Chill for about 30 minutes, stirring several times. Pour into dessert glasses. Chill for another 30 minutes. In the meantime, cut the passion fruit in half, scrape out the seeds and allow to drip off a little. Sprinkle over the cream and serve decorated with lemon balm as desired