Scrape the seeds from the centre of each vanilla bean half then put milk, cream, vanilla seeds and bean halves in a saucepan. Bring to a boil, stirring over medium low heat. Strain the milk mixture into a jug and discard the vanilla bean.
Whisk sugar and egg yolks until thick and creamy. Now, whisk in hot milk mixture gradually into the creamy egg mixture.
Pour the custard mixture into the saucepan and place over low heat. Cook, stirring with a wooden spoon until mixture is thick enough to coat the back of a spoon.
Pour mixture through a fine sieve into a bowl, then stand the bowl in a larger bowl that is placed in a basin of ice-cold water.
Stir the custard frequently for about 10 minutes or until mixture cools - this will stop the custard cooking and splitting on cooling. Cover custard surface with plastic wrap to prevent custard from forming a skin.