Clean and wash the rhubarb and cut it diagonally into pieces about 3 cm long. Place in a bowl. Sprinkle 2 tablespoons of sugar over it and mix into the rhubarb pieces. Allow to soak until ready for use
In a bowl, whisk the fat, 350 g sugar, vanillin sugar and salt with the whisks of the hand mixer until creamy. Separate 5 eggs. Stir 5 egg yolks and 5 eggs one after the other into the fat-sugar mixture. Stir in the vanilla sauce as well. Mix flour and baking powder and stir into the mixture quickly.
Grease a fat pan of the oven (36 x 41 cm) and dust with flour. Add the dough and smooth it down. Spread rhubarb on top. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for about 30 minutes. Shortly before the end of the baking time, beat 5 egg whites with the whisks of the hand mixer until stiff, add 300 g sugar and beat until the sugar has dissolved. Take out the cake. Increase the oven temperature (electric oven: 200 °C/ circulating air: 175 °C/ gas: see manufacturer). Spread the meringue loosely over the cake. Bake for another 10-15 minutes.
Shortly before the end of the baking time, beat 5 egg whites with the whisks of the hand mixer until stiff, add 300 g sugar and beat until the sugar has dissolved. Take out the cake. Increase the oven temperature (electric oven: 200 °C/ circulating air: 175 °C/ gas: see manufacturer). Spread the meringue loosely over the cake. Bake for another 10-15 minutes. Take out and let cool on a cake rack