Mix the sour cream, vanilla yoghurt, sugar and vanilla sugar together. Soak the gelatine in cold water. Express and dissolve in the hot rum. Let cool for 10 minutes and stir into the cream mixture. Whip the whipped cream firmly and fold in. Line a casserole dish with ladyfingers, spread half of the raspberries over it, brush with cream, spread the remaining raspberries over the top and finish with cream. Chill for 2 hours.