Grind the ladyfingers in the food processor and mix with the butter. Pour into a springform pan brushed with oil and press down firmly. Keep a handful.
Let the jelly soak with water for 10 minutes and heat, but do not boil. Mix the Philadelphia cheese with 3-4 tablespoons of sugar, vanilla sugar and lemon juice. Fold in the dissolved jelly. Fold in the whipped cream and then the mandarins. Pour the cream into the mold on the cake base. Scatter the remaining biscuit crumbs on top.
Prepare the cake the day before and put it in the fridge overnight.