Wash, clean and cut the rhubarb into pieces. Mix rhubarb and vanillin sugar. Separate 2 eggs. Chill the egg whites. Mix fat, 250 g sugar and 1 pinch of salt with the whisk of the hand mixer. Stir in 2 eggs and egg yolks one after the other. Mix flour, pistachios and baking powder and stir in alternately with the milk.
Put the sponge mixture into the greased fat pan of the oven (32 x 39 cm) and smooth it down. Spread rhubarb evenly on top. Beat 3 egg whites until stiff, add 150 g sugar. Beat the meringue until the sugar has dissolved. Pour the mixture into a piping bag and spray onto the cake in a grid pattern. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 25-35 minutes. Remove from the oven, place on a cake rack and allow to cool
30 minutes waiting time