I went to look up the recipe I've used in the past, Big Bob Gibson's, and it has changed over the years.
The latest iteration
Big Bob's Gibson's White Sauce Recipe: Recipes: Food Network is closer to the way I adapted the earlier version (I wonder if they changed their recipe after they read my online edits to it :-) ) I do not use cider, and I substitute hot sauce for cayenne.
Gibson's restaurant uses it on their BBQ chicken - I like it as a table sauce with brisket.
Lee