Fill a large bowl or dishpan with ice, and place a pot or bowl large enough to hold all of your ingredients into the ice. This is where you will pour the sauce when finished.
Place the milk and vanilla beans into a large saucepan or pot over medium heat, and bring to a boil. While waiting for the milk to boil, whisk together the egg yolks and sugar in a medium bowl until thick and creamy.
When the milk comes to a boil, gradually whisk it into the egg whites, stirring constantly so that the hot milk does not scramble the yolks. Then pour the mixture back into the pot and place over low heat. Remove the vanilla beans. The seeds may be scraped out, and returned to the sauce if desired.
Stir constantly over low heat until the cream coats the back of a metal spoon. Do not allow it to boil. This part is very tricky, it is a fine line between done and overcooked. If you can, use a thermometer to cook the mixture to 182 degrees F (83 degrees C). If you start to see any signs of egg lumps, immediately remove from the heat.
Pour the sauce into the awaiting container in the ice bath. This will stop the cooking process. If your sauce had small chunks of egg, you may strain it through a sieve on its way into the container.
