Heat the cream in a saucepan. Break the dark chocolate into pieces, add to the cream and melt while stirring. Stir in cardamom. Put the chocolate cream in a mixing bowl and chill for about 3 hours. Break white chocolate into pieces.
Melt white chocolate and oil in a bowl over a warm water bath. Spread the chocolate thinly on a cool marble board or the back of a baking tray and put in a cool place. Once the chocolate is firm, scrape with a spatula or pallet of rolls. Put the rolls in a cool place. Whip the cold chocolate cream with the whisk of the hand mixer until semi-stiff, fill into suitable moulds and sprinkle with chocolate rolls
waiting time approx. 3 3/4 hours