Get a shank or bones. Roast with some carrots, celery, onion, mushrooms, thyme and bay leaf.
Put into a pot and simmer 4 hours.
Strain and skim fat. Add splash of red wine and reduce.

I'm sous viding prime rib and need some au jus. Anyone have a good recipe?
My default would be a packet, esp without a lot of pan drippings.