Beat the yoghurt with the sugar and vanilla sugar until foamy and fold in the gelatine, (dissolved according to the instructions on the packet), the stiffly beaten egg white and the coconut liqueur.
Turn into a freezing bowl and put in the freezer to begin freezing, stirring frequently. Puree the blueberries and push through a sieve.
Mix with the sugar, Cassis and lemon juice and beat until foamy. Take the yoghurt ice cream out of the freezer and mix with the blueberry pulp. Put into individual glasses, if desired, and freeze for at least 3 hours.