My mother always selected roast beef by the number of ribs. She said that a minimum of 3 ribs meant that the piece would be large enough to cook as desired. Smaller pieces tended to become overdone. The following applies to boneless rolled rib roasts also. If you get a very large roast, you can make wonderful things from the leftovers, like Beef Stroganoff, Roast beef sandwiches or hash.
Recommend you read attached pdf: Knowledge - Cooking Prime Rib
Anyway, a three rib roast might weigh 4 lbs. For a Christmas dinner, I usually get a 5 rib roast. This weighs in at about 6-7 lbs. Obviously, this varies a lot. The usual suggested cooking time is 20 minutes per pound. Using a meat thermometer is a good idea and I usually cut a slice part way through near the edge when I think it’s about time. Approximate time is about an hour for a small roast, and up to 2 hours for the biggest.
If it’s pretty pink, but not purple, I take it out. The roast will continue to cook for a while after being removed and if you find it’s too rare after you start slicing it, you can always put it back in and cook it some more. Too well done is not a disaster, but is disappointing.
For a large roast, I often ask the butcher to remove the roast from the ribs and trim and tie it up, so it is easier to serve, but I use the rib section as a base for roasting it. It makes a sort of rack and adds to the often meager drippings for making gravy. Also, the cooked ribs are great to eat or for making soup. If you want to just cook it as it comes, with the ribs still attached, you may need to put the rib section back in the oven so it gets more well done–this can be the next day if you want.
Season roast liberally with salt, (I prefer sea salt) garlic powder, Italian herb seasoning and fresh ground pepper. Rub it all over the surface. When roast is done, remove to a platter while making the gravy.
Preheat oven to 425 degrees. Sear for 15-20 minutes, then decrease heat to 325. Cook for about 13 minutes per pound if the roast is at about room temperature. Also, the meat will cook more evenly if it is allowed to come to room temperature before roasting. Learn to rely on a good oven thermometer.
There is a long discussion of making gravy in the recipe for leg of lamb. But the main thing with roast beef is that there is often not enough brown stuff in the pan to make a lot of gravy. You have to pour off a ton of fat. I usually end up with about 2 -3 tablespoons of fat left in the pan, then add about 3 tablespoons of flour, either directly in the pan or using flour and water mixed together ahead of time (best bet for smooth gravy). Start with a small amount of fat. This way you won’t end up with a large amount of weak gravy. The volume for any sauce or gravy is based on equal parts fat and flour first, cooked, then a volume of liquid is added. Example: 2 tablespoons of fat, 2 tablespoons of flour and 1 cup liquid.
As the gravy thickens, stir and scrape the bottom of the pan to loosen all the good brown drippings. When you are finished, transfer to a saucepan and keep warm. I don’t usually strain gravy, but you can if it seems lumpy. I have never been too happy with adding flavoring to make gravy more tasty. You can add a little Worcestershire or beef “base” Williams Sonoma demiglace can add a good amount of flavor. Some of the beef base or beef tea type products are really too salty.
Horseradish is good with roast beef also. I use commercially prepared horseradish.