Beat the eggs, 9 tablespoons cold water, 150 g sugar, 1 pinch of salt, vanilla sugar and sponge cake perfectly with the whisk of the hand mixer on the highest setting for about 5 minutes until frothy.
Mix flour, baking powder and poppy seeds and fold into the egg foam mixture in approx. 3 portions. Spread the mixture on a baking tray lined with baking paper (approx. 35 x 40 cm). In a preheated oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see
manufacturer) bake for about 10 minutes. Remove from the oven. Turn the sponge onto a damp tea towel and remove the baking paper immediately. Let the sponge cake cool down.
Drain the mandarins well and collect the juice. Soak gelatine in cold water. Whip cream until stiff. Mix quark, yoghurt and 2 tbsp. sugar. Chop 2 tbsp. mandarins and stir into the cream.
Cut the sponge cake in half crosswise to make 2 smaller plates. Place each plate on a board or tray (should fit in the refrigerator). Squeeze out the gelatine and dissolve at low heat.
Stir in 4-5 tablespoons of the quark cream by the spoonful, then stir into the rest of the cream.
Fold in cream in portions. Spread the cream evenly on the 2 pastry plates, carefully spreading it along the edges. Spread the mandarins on top. Chill the cake for approx. 2 1⁄2 hours.
1⁄2 l Measure out the tangerine juice. Mix the cake glaze and 2 tablespoons of sugar in a small pot. Stir in tangerine juice bit by bit. Heat while stirring and bring to the boil briefly. Remove from heat and let rest for 4-5 minutes.
Spread the icing evenly on the mandarins, chill again for about 1 hour. Chop the pistachios. Cut cake into pieces and sprinkle with pistachios.