In a bowl, soak the gelatine leaves in cold water until supple.
In a small heavy pan, bring the whipping cream to the boil with the vanilla pod and seeds from the cardamom pods and simmer on a very gentle heat a few minutes to infuse. Take out the vanilla pod and the cardamom, and put these to one side.
Make a ganache by pouring
Squeeze out excess water from the gelatine leaves and drop into the remaining hot cream. Stir until completely dissolved. Stir in the saffron and leave to steep for a minute for two. Allow to cool.
Fold into the cooled ganache, sprinkling in the lemon zest as you do. Pour the mixture into 6 small timbales, clean yoghurt pots or tea cups and chill for at least 2 hours.
To serve, unmould straight from the fridge with the help of quick dip in very hot water if necessary, and accompany with some dark chocolate sauce.