Have ready near the range a fine strainer lined with cheesecloth, suspended over a small mixing bowl.

In a small heavy noncorrodible saucepan stir together the yolks, sugar, and salt until well blended, using a wooden spoon.

In another small saucepan (or a heatproof glass measure if using a microwave on high power), heat the milk, coffee, and vanilla bean to the boiling point. Stir a few tablespoons into the yolk mixture; then gradually add the remaining milk, stirring constantly.

Heat the mixture, stirring constantly, to just before the boiling point (170°F. to 180°F.). Steam will begin to appear and the mixture will be slightly thicker than heavy cream. It will leave a well-defined track when a finger is run across the back of a spoon. Immediately remove from the heat and pour into the strainer, scraping up the thickened cream that settles on the bottom of the pan. Remove the vanilla bean and scrape the seeds into the sauce. Stir until the seeds separate. For maximum flavor return the pod to the sauce until serving time.

Cool in an ice-water bath or the refrigerator. Stir in the optional Kahlúa.