You can make this sauce up to 2 days ahead;
press plastic wrap directly onto the surface to
prevent a skin from forming, and refrigerate.
4 large egg yolks
1/4 cup sugar
1 cup milk
3/4 cup heavy cream
1/2 vanilla bean, halved lengthwise
Whisk together the yolks and sugar in a medium
bowl until pale, about 4 minutes.
Pour the milk and cream into a medium
saucepan. Scrape in the vanilla seeds; add the bean.
Heat over medium heat until just about to simmer.
Reduce heat to low; whisk 1/3 cup into the egg yolk
mixture. Return to the pan. Cook over medium heat,
stirring, until thick enough to coat the back of a
wooden spoon, about 8 minutes.
Pour the mixture through a fine sieve into a stainless-
steel bowl set in a large ice-water bath. Discard
the solids. Chill until cold, stirring occasionally.