Defrost blueberries at room temperature. Peel 50 g chocolate in small rolls with a peeler and chill. Coarsely chop 250 g chocolate and fat and melt over a warm water bath. Coarsely crumble the rusks and put them in a large freezer bag. Crumble finely with a dough roll. Mix rusk and melted chocolate.
Coat the bottom of a springform pan (26 cm Ø) with oil. Add the crumble mixture and press to a smooth base. Chill for about 1 hour. Soak gelatine in cold water. Mix cream cheese, sour cream, sugar, vanilla sugar and lemon juice with the whisk of the hand mixer until smooth. Whip the cream until stiff. Stir in blueberries. Squeeze the gelatine, melt in a small saucepan over low heat. Stir in 5 tablespoons of the cream cheese mixture in portions. Stir into the remaining cream cheese mixture. Fold in cream in portions and spread loosely on the base. Chill for approx. 3 1/2 hours.
Stir in blueberries. Squeeze the gelatine, melt in a small saucepan over low heat. Stir in 5 tablespoons of the cream cheese mixture in portions. Stir into the remaining cream cheese mixture. Fold in cream in portions and spread loosely on the base. Chill for approx. 3 1/2 hours. Remove the cake from the springform pan. Sprinkle with chocolate rolls
waiting time approx. 4 1/2 hours