How to Surely Make a Perfect Medium-Rare Prime Rib Roast + Au Jus!

When I made my prime rib roast for the first time, I bought it pre-seasoned from Costco. (So yes, I cheated), but here’s the directions I followed to make sure my prime rib roast would come out exactly the way I like all my steaks cooked; medium rare.


  • Pre-seasoned prime rib roast from Costco (mine weighed 7lbs)
  • 5 carrots
  • 4 onions (any, I bought a bag of mixed onions and used 2 yellow, 1 white and 1 purple/red)
  • 1/4 cup Beef Stock
  • 1 teaspoon of Corn starch/flour
  • 1 tablespoon of Worcestershire sauce
  • 1 teaspoon salt
  • 1 tablespoon black pepper
  • 1 tablespoon sugar


  1. Pre-heat your oven on BROIL to 500 degrees Fahrenheit.
  2. Peel the carrots & onions. Cutting them to fit UNDER your prime rib roast steadily.
  3. When your oven is ready, place your prime rib roast. Let it cook for 5 minutes PER pound!
  4. After time is up, DO NOT OPEN YOUR OVEN DOOR!!! This is the most important thing to NOT do.
  5. Turn off the heat for your oven & let it sit in there for TWO hours. Remember.. do NOT.. I repeat, DO NOT open your oven door until the timer’s completely up,
  6. After letting it sit for 2 hrs in the oven unbothered, remove it from the oven & remove the prime rib roast from the roasting pan/rack onto a cutting board. Remove the vegetables as well, you’re going to save and use the drippings for the au jus (sauce).
  7. If your roasting pan can handle direct heat from your stove, use it to make the au jus, if not, just transfer the drippings to a pan.
  8. Turn the heat on your stove to medium-high. When simmering, add a teaspoon of cornstarch or flour (whichever works fine) and mix it well. Make sure there aren’t any clumps.
  9. Add the beef stock and let it come to a boil.
  10. Add worcestershire sauce (optional, I just personally think it adds more flavor to the au jus and I just like using it with most of my steaks)
  11. Add salt, black pepper and sugar. I recommend seasoning with these ingredients to your personal liking, so taste testing as you make this sauce is highly recommended.
  12. Also, if you prefer your sauce thicker & gravy-like, feel free to add a little more corn starch or flour. No more than ½ a teaspoon more though.

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