This vanilla custard sauce is a sauce and not meant to be as thick as custard and if meant for purposes when you would like a custard flavor sauce to serve with desserts.
Pour the milk and cream into to a medium-sized saucepan set over medium heat.
If using vanilla bean, scrape the seeds into the pan and then add the bean itself.
Bring the milk to a simmer.
Once heated, remove from heat and set aside to cool for 15 minutes.
Remove and discard the vanilla bean.
In a separate bowl, beat the egg yolks with the sugar.
If using vanilla extract rather than vanilla bean, add vanilla extract to the eggs and sugar. Beat for 3 minutes, until light and foamy.
Gradually stir in the milk, a few tablespoons at a time.
Return the custard mixture to the saucepan and cook over medium heat. Stir constantly until the custard starts to thicken. Do not let the custard come to a boil or else it will curdle.
Once thickened, allow the custard to cool. Custard will thicken as it cools.
Once cooled, refrigerate custard until ready to use.