Place the cream in a thin-sided bowl and suspend over a gently simmering bain-marie, ensuring that the bowl does not touch the water. Heat the cream, add the chocolate and cardamom, melt. Remove the bowl, stir with the whisk on a hand mixer until the chocolate and cream mixture has cooled and solidified a little. Transfer the mixture to a disposable piping bag and chill for approx. 2 hrs.
Pipe balls each approx. 2 cm in diameter onto a piece of baking paper, leave to set in the fridge for approx. 30 mins. Blitz the pistachios in a food processor, place in a deep dish. Separate the truffles from the baking paper, roll briefly between your hands, roll in the pistachios, chill.