Split vanilla bean in half lengthwise. Carefully scrap seeds.
In a saucepan over a medium heat, bring 2 cups heavy cream to a bare boil with vanilla bean and scraped seeds.
Remove cream from heat. While cream is cooling, beat the egg yolks and 1/2 cup sugar in a mixer, until thick ribbons form.
To temper the egg yolks, and keep them from curdling, gradually add 1 cup warm cream to egg mixture, whisking constantly.
Add tempered egg yolk mixture back into saucepan, with remaining cream and stir constantly over a medium heat, until thick enough to coat the back of a spoon.
Remove from heat and strain through a fine strainer. Remove the vanilla pod. (I rinse it off and dry it, then add it to a bowl of sugar)
Cool custard slightly and then cover with plastic wrap to prevent a skin from forming. Refrigerate until ready to use.