Mix the yolk, powdered sugar, vanilla sugar and yoghurt with the mixer. Put the gelatine in a water bath for 10 minutes. Heat the rum and lemon juice, stir in the gelatine, let it cool down a little. Then add drop by drop to the yogurt. Mix everything with whipped cream. Transfer to a bowl and refrigerate for 24 hours.
Then cut out dumplings with a spoon and serve with any sauce.