Get some Orrington Farms Beef Flavored Broth Base & Seasoning 12 oz. Jar, Shelf Stable at Walmart. Mix per label instructions. Thicken just a bit with a flour Roux or Corn Starch if desired. (this will help lower the saltiness of the basic mix.) Don't add any salt unless you are a salt junkie.
Get whatever cut of beef you prefer: Ribeye, Top Sirloin, Prime Rib or even a good Rump Roast roasted slowly in the oven covered with foil and some of the mixed broth base in the pan.
IMO, no matter if you use a bullion or a packaged mix, red wine is a key element for good au jus. Also, homemade au jus is just as easy to prepare:
Beef Au Jus (no drippings used)
2 c beef broth
1/4 cup red wine
1/4 cup chopped red onion
1 tel dill
2 tel butter
1 tsp Worcestershire sauce
1/4 tsp koshe salt
Pepper to taste
Sauté onions until soft, add red wine to deglaze the pan. Lower heat and add butter, wisk until melted. Whisk in beef broth, Worcestershire and kosher salt,
Bring to a boil on high and reduce 5 minutes. STRAIN and serve immediately.
Also, in my opinion, prime rib sliced thin is the only beef to use.
If you actually cook a prime rib, you can add 4 tbl of the drippings with a bit of flour, red wine, beef broth and Worcestershire, simmer until slightly thick.