CrustCrush the biscuits by placing them in a freezer bag and rolling a rolling pin over the bag a few times until the biscuits are crumbled.You can also crush the biscuits in a food processor, but do not let the machine run for too long. Stop when the biscuits are just crushed.Place the biscuit crumbs in a bowl and add soft butter.It is easiest to use your hands to mix the dough. It should not be kneaded but just stirred together.Place the mixture in the bottom of a springform pan and press it out evenly until you have a uniform base with the same thickness throughout. Cheese FillingPut cream cheese, powdered sugar, and vanilla sugar in a bowl.Mix well, preferably with an electric mixer.Whip the cream into stiff peaks and fold it into the cream cheese mixture with a spatula. Do not whisk or stir too vigorously, as that will deflate the whipped cream.Spread the cheese cream over the biscuit base and refrigerate for at least 2 hours. Blackcurrant JellySoak gelatin sheets in cold water for about 30 minutes.Bring the blackcurrant juice to a boil in a saucepan.Remove the softened gelatin from the water and squeeze out most of the water.Add the gelatin to the liquid and stir until it melts.Set the saucepan aside to cool at room temperature until the liquid is lukewarm.Pour the nearly cooled blackcurrant jelly over the cheesecake and return it to the refrigerator.Let the cake chill for at least another 2 hours until the jelly is completely set.Serve the cake as it is or garnish with fresh berries.