In a medium mixing bowl, using a whip, whisk together the egg yolks and sugar until they are very pale yellow and smooth.
In a medium saucepan, bring to a boil the heavy cream, sour cream, and vanilla bean with its scrapings. Whisk about half into the egg yolk mixture until well combined, then pour back into the saucepan. Over medium heat, stirring constantly with a wooden spoon, cook until the mixture heavily coats the back of the spoon. Don't scramble the eggs.
Strain into a clean bowl and set the bowl over ice cubes and cold water until chilled, stirring occasionally. Refrigerate, covered, until needed.
Note: To make coffee Creme Anglaise, substitute 1/4 cup crushed coffee beans (with or without caffeine) for the vanilla bean. Bring to a boil and let steep in the cream mixture, covered for about 10 minutes. When well flavored, whisk into the egg yolks. then continue with recipe
To crush coffee beans, place in a plastic bag, close the bag, and heavily press a rolling pin over the beans. Do not grind the beans because this will darken the Creme Anglaise.