I love this sauce. It may have been part of the first meal Bill cooked for me...or maybe the second. It comes from Betty Crocker's Mexican Made Easy - published in 1993, I think it may be out of print now. Bill bought his copy for $2.99 at a Building 19 store an eternity ago.
Anyway, from Chapter 2 in the book - "Sizzling Sauces and Sides" - the description for Green Sauce is as follows:
"This is a suave chile sauce, slightly chunky and rich with cream."