Line the bottom of a springform pan (26 cm Ø) with baking paper. Separate the eggs. Beat the egg whites until stiff, adding salt, 100 g sugar and 1 packet of vanilla sugar. Beat the egg yolks separately into the mixture. Sift the flour and baking powder into it and fold in. Brush into the mould. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/gas: level 2) for about 20 minutes. Cooling down
Clean, wash and chop the rhubarb. Measure out 800 g rhubarb. Boil up with 100 ml water, simmer open for 8-10 minutes. Stir in 200 g sugar. Mix pudding powder and 6 tbsp (60 ml) water. Stir into the compote and bring to the boil briefly. Let cool down for about 20 minutes. Close a cake ring around the cake base. Spread the compote on top and chill for about 1 hour
Soak the gelatine in cold water. Mix buttermilk, 4 tablespoons sugar and 1 packet vanilla sugar. Squeeze the gelatine and dissolve at low heat
Stir in 6 tablespoons of buttermilk by the spoonful, then stir into the rest of the buttermilk. Chill until it begins to gel. Whip 150 g cream until stiff. Stir into the buttermilk. Spread on the compote. Keep cold overnight
Whip 100 g cream until stiff, warm up jam. Decorate the cake with cream tuffs, jam and lemon balm
If the compote is very liquid, simply take 2 packets of pudding powder instead of 1