Soak the gelatine in cold water for 5 minutes or until softened.
Place the chocolate, cardamom and 500 ml (17 fl oz/2 cups) water in a double boiler over simmering water and stir until melted and smooth. Squeeze out the excess water from the gelatine, add the gelatine to the chocolate mixture and stir until dissolved. Pass through a fine sieve. Place in a cream canister and charge twice. Refrigerate for 1 hour or until set.