Used the "Method X" method for cooking a prime rib that I saw online.
The method:
1) Let rib roast sit out overnight (at least 6 hours) so it gets to room temperature
2) Preheat oven to 500 degrees
3) Cover your roast in whatever seasoning you prefer. This particular method calls for "seasoned butter", which is 1/4 cup butter, 1 tsp salt, 1 tsp pepper, 1/2 tsp cayenne, and 1 tsp of Herb de Provence. Smother the butter mixture all over the roast and then top with additional salt and pepper
4) Take exact weight of roast and multiply by 5. This is the amount of time to cook at 500 degrees. (Ex: a 5 lbs roast you would cook at 500 degrees for 25 minutes. A 7 lbs roast for 35 minutes).
5) After time has expired, turn oven off, but DO NOT OPEN the door. Leave roast sit in oven for an additional two hours.
6) After two hours have passed, you will have a perfect medium-rare prime rib.
I used this method yesterday to make a 9lb prime rib. I have also used this method 2 other times. It works perfectly. Easy and as long as you follow the rules (get meat to room temp and don't open oven) you will be very happy with results
The only thing i will say is when u have a cut as big as I did yesterday and you have it on 500 for 45 minutes, you better get some fans going because that thing will smoke out your kitchen.