See Mark Vogels article on Custards
1 vanilla bean or 1 tablespoon vanilla extract
Half cup sugar
2 cups milk, cream, or combination thereof
4 egg yolks
Split the vanilla bean, scrape out the seeds and place them in a saucepan.
Add half of the sugar and all of the milk. Heat, while whisking, until the mixture becomes hot but not boiling.
Remove from the heat.
Whisk the eggs in a bowl, gradually adding in the other half of the sugar until they form a ribbon.
Slowly whisk half of the hot milk mixture into the eggs.
Then pour the egg mixture into the saucepan with the rest of the milk.
Over low heat, constantly whisk until it reaches 170-175 degrees or coats the back of a spoon, about five to eight minutes.
Do not boil it.
Strain the sauce.
Chill it in the fridge with a piece of plastic wrap right on the mixture to prevent a film from forming.