Separate eggs. Beat egg yolk and sugar until frothy. Beat the egg whites until stiff, allow the vanillin sugar to trickle in. Sift flour and baking powder. Fold into the egg yolk mixture with the beaten egg white. Spread on a greased fat pan (approx. 32 x 39 cm). Bake in a preheated oven (electric cooker: 200 °C / fan oven: 175 °C / gas: level 3) for approx. 15 minutes. Let them cool down
Drain the tangerines, collecting the juice. Measure out 1/2 litre of it. Spread the mandarins on the cake, except for about 36 pieces for decoration
Mix the pudding powder and 8 tbsp. mandarin juice. Bring orange juice and remaining tangerine juice to the boil. Stir in the pudding powder. Bring to the boil again briefly. Spread the pudding immediately on the tangerine layer and let it cool down for about 1 hour
Whip the cream until stiff, adding icing sugar and cream firming agent. Spread 3/4 cream on the pudding. Place approx. 36 biscuits on top of the cream layer, placing the biscuit side or the chocolate side up as desired. Decorate with the rest of the cream and mandarins