1.Split 1 vanilla bean in half lengthways; scrape seeds into medium saucepan, add pod, 1½ cups milk and 1 tablespoon caster sugar. Boil, then strain into large jug. Discard pod.
2.Whisk 4 egg yolks and ¼ cup caster sugar in medium heatproof bowl set over medium saucepan of simmering water until thick and creamy; gradually whisk in hot milk mixture.
3.Return custard mixture to pan; stir, over low heat, until mixture is thick enough to coat the back of a spoon. Refrigerate custard about 1 hour or until cold.
If the custard splits or curdles, try chilling it and then blending or beating with a stick blender or hand beaters.Note