This method for cooking a roast will give you an even temperature throughout the entire piece of meat. I also tell how to choose the best roast to cook.
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2. When purchasing a roast, purchase one rib per person if you're having "MEAT DAY". If your serving it with sides, you should probably have about 3/4 pound per person. Be sure to ask your guests how big they want their piece when you cut it. I don't usually serve it with the bone (it takes up too much room on the plate.
3. Prepare the Roast by inserting slivers of Garlic all around, oil, then rub lots of Salt, Pepper, and Blacken into the meat, lay the sliced onions on top after you have placed it on a rack in a baking dish. Insert a meat thermometer into the thickest part of the meat in such a way that you will be able to see it through the window in the door without having to open it.
4. Place the meat in the oven for 20 minutes then turn down to 275 deg., without opening the door. Cook an additional 1 3/4 hours or until the meat thermometer reads 110 - 120 degrees, 110 degrees will give you a rare roast, pictured, and 120 degrees will end up med rare. If you like well done meat, don't waste your money on a prime rib, purchase a chuck or a top round and make a pot roast out of it.
Cooking time should not change because you have a larger piece of meat, because, although the meat will be longer, the diameter will usually remain about the same. This timing works good for a roast that is 6" - 7" in diameter.
5. This temperature (120 degrees) makes for a medium rare roast. Remember, don't cook it rare because it'll be quite tough.
6. Take the roast out of the oven and let it rest for 20-30 minutes loosely covered with alum. foil; this allows the roast to finish cooking and the juices to re-distribute. Don't worry about letting it rest too long because there isn't such a thing with Prime Rib (it's usually served at room temperature). Letting it rest, covered, lets it finish cooking. If you leave the thermometer in, you'll notice that it will actually go up about 10 degrees. If you wish to make gravy (sauce), you can set the meat on a separate platter, cover with aluminum foil, and use the pan drippings for the base of a sauce.
7. If you don't have a rack to place the meat on, you can use rough cut carrots and onions. Make sure you spray some Pam on the pan prior to putting the vegetables inches Later, you can place these vegetables into the pot you're making the gravy in, and grind them up with an immersion blender to become part of the gravy / sauce.