Grease the springform pan (approx. 26 cm Ø). Separate the eggs. Cream fat, 125 g sugar, 1 vanilla sugar and 1 pinch of salt. Stir in the egg yolks one by one. Mix flour and baking powder and stir in briefly, alternating with the milk.
Spread half the dough into the mould. Beat the egg whites and 1 pinch of salt until stiff, adding 200 g icing sugar. Spread half of the beaten egg white slightly wavy on the dough, leaving about 2 cm free around the edge.
Bake in the preheated oven (electric cooker: 175°C/circulating air: 150°C/gas: level 2) for approx. 30 minutes. Cool down. Bake a 2nd base from the remaining dough and beaten egg white in the same way.
Clean, wash and slice the rhubarb. Mix rhubarb slices (600 g), 125 g sugar and cherry nectar in a pot and bring to the boil while stirring. Simmer the rhubarb slices for about 4 minutes until they start to crumble.
Let the compote cool down.
Soak gelatine in cold water. Mix yoghurt, 50 g sugar and 2 vanillin sugars. Squeeze the gelatine, dissolve over low heat. Stir in 2-3 tbsp. yoghurt, then stir into the remaining yoghurt.
Stir in rhubarb compote. Chill until the rhubarb cream begins to gel (takes approx. 10 minutes to approx. 45 minutes depending on the variety).
Whip the cream until stiff, fold into the cream. Close the cake ring around a cake base. Spread the cream on top. Place the 2nd cake base on top. Chill for about 4 hours. Dust with some icing sugar.