Prime Rib...

rocks.

My demo today was a perfectly roasted 6 lb prime rib.

How to do it:

If it hasn't been done already, have the meat cutter cut off the bone and tie it back on for roasting.

The Rub:

3 TB sugar
3 TB Kosher salt
3 TB course ground pepper
1 TB Rosemary ground up with a mortar and pestle
5 Garlic cloves squished through a garlic squisher

Add olive oil to form a paste and rub all over your prime rib. Cover with plastic wrap.
Allow roast to come to room temperature (about 4 hours)

 The Searing

Preheat oven to 460.  I've found that any higher temp has a tendency to burn the garlic. 
Place roast in roasting pan bone side down and do not cover. 
Cook roast for approximately 5 minutes for each pound.

The Roasting

After searing roast, open oven door to cool oven and set temperature to 250.
When oven has cooled somewhat, close door and roast for 20 minutes per pound.

Important Info for Success

You must use a meat thermometer when cooking prime rib.
For medium rare, cook to internal temperature of 135.
Take temperature several different places and make sure you aren't touching the bone.
The temperature of the roast will continue to go up after it is removed from oven, so you'll want to take it out of the oven at about 130.
Cover it with foil and let it rest on the counter for 30 minutes.

While the roast is having a wee rest, scrape any burnt thingy's out of the bottom of the roasting pan and discard.   Add a bit of beef soup base and some water and heat on stove for your au jus.    I prefer Better Than Bouillon Beef Base.
Remove the strings from your roast and the bone will drop off.
Slice (always at the table for drama) and enjoy! 

The only mistake you can make with a good prime rib is overcooking.  It is way better to err on the side on under-done since you can always stick it back in the oven for 10 or 15 minutes.  However, once that expensive and luscious piece of meat is over-cooked, there's no going back.

Here's another method I use:

Notice he sears at 500 degrees because he is not using fresh garlic.