For the base, divide chocolate into pieces and melt in a hot water bath with coconut oil. Crush the cornflakes slightly with your hands in a bowl and mix with chocolate. Press the mixture in the cake ring (26 cm Ø) to a flat base. Chill for about 30 minutes.
For the cream, soak 8 sheets of gelatine in cold water. Mix sour cream, lemon juice, 125 g sugar and vanilla sugar. Whip the cream until stiff. Squeeze 8 sheets of gelatine, dissolve and mix with 2-3 tbsp. sour cream, then stir into the rest of the cream. Fold in the cream. Spread the cream on the base until smooth. Chill for about 2 hours.
For the berry mirror, soak 2 sheets of gelatine in cold water. Select the berries and wash them if necessary. Puree with 1 tbsp. sugar and pass through a sieve. Squeeze out the gelatine, dissolve and gradually mix with the berry puree.
Spread the fruit mass over the cream, chill the cake for another 2 hours. Remove from the ring and serve.