We have a friend here in the U.S., that owns a restaurant. He serves the best Prime Rib (as your cut is called here) anywhere. He does it differently and we tried here at home and use this method on all roast beef, but especially Prime Rib.
Take the cut out of the fridge at least two hours before cooking... even longer is better. Turn you oven on to a temperature of 550 degrees (F). No typo here Five Hundred Fifty degrees Fahrenheit (228 C). (A note; some ovens will only reach 500 degrees F, in which case add 5 minutes to total cooking time). While you're waiting for it to reach that temperature, place the roast, bone side down in the heaviest roasting pan you have. Use any rub, but especially fresh ground black pepper, but spare on the salt, since that draws moisture out of the roast. (We use thyme and a little mustard powder). Rub the ends with any oil or butter.
Place the rib in the oven and cook for 5 minutes per pound for rare and 6 minutes per pound for medium. (Note 2; You can simply multiply the weight by 5 which will give you the total cooking time before shutting off the oven. Example, a 6 pound roast would require 30 minutes).
NEVER open the oven... NEVER... when the cooking time is reached, turn the oven off and leave at least two hours or until the temperature has completely dissipated. Remove and cover with foil and let it rest at least 30 minutes before slicing.
We've never had this method fail. The drippings, by the way, make a wonderful aus juice or gravy...