I don't advise moist heat at all- do them both in the oven if you can. A salt dome isn't necessary IMO. I've made literally tons of prime rib in restaurants, the bulk of it in a conventional oven (although a convection oven is nice for browning the herb/garlic crust).
Technically you're better off using high heat at the end, not the beginning- just ask Alton Brown.
But high heat to start is okay, too. I suggest a bit of Montreal Seasoning
or Canada's Best Steak Seasoning
to start, along with Classic Herb Seasoning
. If you can't find that, go with kosher salt or Lawry's
salt along with fresh ground pepper. The last thing to add should be chopped garlic, enough to liberally coat the whole thing, although not too thick or it won't stick thru out the cooking process.
I suggest a pan with a roasting rack so air can circulate around the roast (yes, a prime is a roast). I'd suggest very high heat to start (say, 450) for about 30-40 minutes to brown the garlic a bit. Then lower the heat to 275-300 degrees. You'll probably have the best results if you use an electronic temp probe with a temperature alarm, like Kitchenaid makes. They're only about $20, and you'll use it all the time. Stick the probe in the end of the prime, right straight in and parallell to the roast in the thick part. Then set the temp alarm for about 5-7 degrees less than you want the prime to be. This way once it goes off, you can take it out and let carryover bring it up to the desired degree of doneness.
Using this method, the middle will be fairly rare but you can get some doner slices off the ends (and the end cuts will provoke fights as people vie for their chunk!
). Cooking at lower temps will result in a prime that's less "bulls-eyed", meaning it will cooked pretty evenly as opposed to being very red in the middle and very done on the outside. The hotter you cook the more you'll get this "problem" with your roast. Some like it that way, though- it depends upon if your guests like it really rare or not.
Try to buy the best meat you can get- you can't do much to jazz up bad meat. A real butcher shop is your best bet unless you know of a good market or have access to your own supply. Most true prime grade goes to restaurants and higher-end specialty butcher shops. I prefer to season the loin and let it rest uncovered in the fridge overnite if I can. For best results, remove the meat a couple hours before roasting- it's ideal if the meat is near room temp when you cook it.
Lastly, I like to serve prime on demiglace, au jus, or with a side of horseradish cream. This is just sour cream with minced horsey added. It's a wonderful accompaniment to good beef.
Good luck with your prime, and happy holidays!