Directions

1. Whisk yolks and sugar in a small bowl. Mix cornstarch and flour in another small bowl. Bring milk, salt, and spices to a boil in a medium saucepan. Remove saucepan from heat. Whisk cornstarch mixture into yolk mixture, and then immediately whisk 2 tablespoons milk mixture into yolk mixture. Whisk in remaining milk mixture in a slow, steady stream.
2. Return mixture to saucepan. Cook over medium heat, whisking constantly, until it begins to thicken and registers 160 degrees on a candy thermometer, 1 to 2 minutes.
3. Strain mixture through a fine sieve into a heatproof bowl, and whisk in vanilla and butter until smooth. Press a piece of plastic wrap directly on surface, and refrigerate until cold and thick, at least 1 hour (or up to 1 day).