Bill here's one I've used as a starting point. You can add more or less butter, depending on your taste or use margarine, which I do. Olive or some other oils work too, equal amounts of flour and the fat. Using buttermilk adds some flair instead or normal milk.
Heating the flour and fat make a roux, I like to make mine a bit brown for more flavor, but the browner it is, the less thickening power the flour has. I usually add more beef too, letting it cook a few minutes on low to extract the beef's flavor.
Creamed Chipped Beef Recipe - Food.com - 269872
Tip: Add the milk slowly stirring constantly to blend better.