Melt the butter in a small pot. Remove from the heat and let it cool down a little. Pour the lady fingers into a freezer bag. Close the bag with a rubber band. Crush the sponge cake with a dough roll
Put the lady fingers and butter in a mixing bowl and mix well. Coat the bottom of a springform pan (26 cm Ø) with oil. Press the crumb mixture evenly with your hands to a firm base. Chill for about 45 minutes.
Pour mandarins into a sieve and drain well. Put the sour cream, yoghurt and pudding powder into a mixing bowl and mix well with the whisks of the hand mixer (not too long, otherwise it is no longer spreadable). Pour onto the crumb base and smooth down. Spread the mandarins evenly over the crumb base.
Mix the sugar and cream setting agent. Whip the cream with the whisk of the hand mixer until stiff, allowing the sugar mixture to trickle in. Spread loosely on the mandarins. Chill for about 45 minutes.
Cut well chilled chocolate into fine pieces. Remove the cake from the springform pan, place on a cake plate and decorate with the chocolate
waiting time approx. 1 1/2 hours