Place the cream and vanillabean in a saucepan over high heat. Stir continuously until the mixture comes to a boil. Set aside, off the heat, to infuse for 5 minutes.
In the meantime, whisk the egg yolks and sugar together.
Prepare an ice-water bath in a large bowl capable of safely holding the saucepan and set aside.
When the vanilla has been infused, discard the bean. Slowly whisk the hot cream into the egg-sugar mixture.
Return the cream mixture to the saucepan and place over high heat. Whisk continuously until the mixture thickens. Transfer the saucepan to the ice-water bath and continue whisking until the sauce is quite cool.
Pour the sauce into a gravy-boat and chill in the refrigerator until needed.