Split the lengthways with the tip of a knife, then lay it on its back and run the knife along the pod to scrape out the seeds.
Pour the and into a saucepan over medium-high heat. Add the vanilla seeds and the scraped pod (or keep the pod aside to make vanilla sugar in a jar of sugar instead). Bring up to a simmer, then let it simmer for 5 minutes to draw out the vanilla flavour.
Meanwhile, in a large bowl, whisk the with using a whisk until pale and silky.
Whisk in until there are no lumps.
Temper the eggs: whisk a splash of the hot milk mixture into the egg yolks so the eggs aren't shocked. Once combined, pour the egg mixture back into the saucepan with the rest of the milk and cream (removing the vanilla pod first if you like).
Cook over a low heat, stirring in figures of eight so it heats evenly and gently, for 3 minutes , until thickened.
Check it's ready by dipping a spoon in the custard and running a finger through the coating on the back
