Crush the cardamom pods, tip them into a saucepan and mix in the cream. Set over a low heat, bring to the boil, then remove from the heat. Cover and leave to infuse for one hour. Meanwhile, find two large bowls, one of which will sit comfortably inside the other. Fill the larger bowl with ice and rest the smaller one on it. Set aside.
Whisk the egg yolks with the sugar until they become pale and fluffy, then slowly stir in the cardamom cream. Return to a clean pan and place over a low heat. Keep stirring with a wooden spoon until the mix forms a thick custard. This will take between 10 and 20 minutes. Do not let the custard boil or leave it unattended at this stage, as it can easily split.
As soon as it forms the thick custard, remove from the heat and tip into the bowl sitting on the ice. Keep stirring until it is tepid, then strain into a clean container, cover and chill.
Once cold, process the custard in an ice-cream maker, according to the manufacturer's instructions.