Make a roux sufficient to cover the bottom of your soup pot and cook until it is not floury any more. Whisk in a quart or more of chicken broth and simmer.
In another bowl, mix together two eggs, mustard to taste (use a mustard you like the taste of. Probably not that runny yellow stuff. I use a cracked mustard because I like the texture of the seeds in the finished product, but I have seen it done with French's and it worked okay.) and milk or cream (a few cups--about as much as the stock). Temper this mixture with the roux and stock, and then whisk it into the remainder of the roux mixture. heat through to thicken and blend flavors.
I learned that one when I was in the Canton of Fennbrycg. The Baron used to make it for Simple Faire, and we'd all gorge on it so thoroughly nobody ever ate the fourth remove.