Mix flour, baking powder, sugar, salt and vanillin sugar. Add quark, oil and milk. Knead to a smooth dough with the dough hook of the hand mixer. Knead again briefly with your hands
Halve the dough, form into 1 roll each and roll out lengthwise on a floured work surface (10-12 cm x 30 cm) and place on a baking tray lined with baking paper. Mix sour cream and pudding powder, spread on the flat cakes
Clean, wash and cut the rhubarb into pieces and spread on the cream. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 15-20 minutes until brown. Take out the flat cake, let it cool down
Bring the jam to the boil in a small pot, spread the rhubarb pieces with it. Chop the pistachios. Sprinkle the flat cake with pistachios and chocolate shavings
Waiting time approx. 1 hour