Add the vanilla bean and seeds to the milk, bring to a gentle boil and allow to infuse for ten minutes. Meanwhile in a heatproof bowl whisk the egg yolk with the sugar until it begins to turn a pale colour. Strain the milk into a jug to remove the vanilla pod, pour back into the suacepan, add the iota carrageenan and whisk over a medium heat until the milk begins to boil. Pour the hot milk over the egg yolk and sugar, whisk then pour into serving dishes. The custards will set within 10-15 minutes and can be served cold or warm sprinkled with a little freshly grated nutmeg