Slit the vanilla pod lengthways and place it in a saucepan. Pour the cream into the pan, then bring almost to the boil. Take off the heat and allow to stand for 15 minutes. Lift the pod out of the cream and, holding it against the side of the saucepan, scrape the black seeds into the cream. Discard the rest of the pod.
Use a fork to mix together the egg yolks and caster sugar in a bowl. Reheat the cream, then gradually mix it into the eggs and sugar. Strain the mixture back into the saucepan.
Place 6 ovenproof ramekins in a roasting tin, then divide the custard between them. Pour warm water around the dishes to come halfway up the sides, then bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20–25 minutes until the custard is just set with a slight softness at the centre.
Leave the dishes to cool in the water, then lift them out and chill in the refrigerator for 3–4 hours. About 25 minutes before serving, sprinkle with the icing sugar and caramelize using a blowtorch (or under a hot grill), then leave at room temperature.