Lightly oil a 20cm (8 inch) loose-bottomed spring form clip tin. Mix together the crushed biscutis and melted butter, press the mixture into the base of the tin and smooth level. Beat the Quark in a mixing bowl to soften. Stir in the melted chocolate and gelatine then carefully fold in the whipped cream retaining as much volume as possible. Strain the defrosted summer fruit mix reserving the juice. Lightly stir the strained fruit into the cream mixture, until just mixted in. Spoon the mixture onto the biscuit base and smooth level. Cover and chill in the regrigerator while the glaze is made. Meanwhile, blend a small quantity of the reserved juice with the arrowroot to form a smooth paste. Place the remaining juice in a small saucepan and stir in the blended arrowroot. Bring gently to the boil over a moderate heat, stirring continually until the mixture thickens and is smooth, clear and glossy. Allow to cool. Spread the glaze evenly over the top of the cheesecake right to the edges. Gently shake the tin to ensure the surface of the glaze is totally smooth and glass-like. Chill for 2 hours until firm and totally set. Carefully remove the spring form tin, using a palette knife to free the sides if necessary. Remove the cheesecake from the tin base and slide onto a serving plate. NOTES : A sumptuous combination of summer fruits and white chocolate in a cheesecake mixture on a crisp biscuit base.