15 Pound Prime Rib Roast
So you bought a 15 pound prime rib roast because you wanted leftovers or you’re having a lot of guests. It’s 5am on Christmas morning and you are googling how long to cook a 15 pound prime rib roast. One article says 8 hours and the next says 90 minutes. To make things more confusing, you keep coming across the term “reverse sear”. Save this recipe and go back to sleep, this 15 pound prime rib roast recipe is tried and true and has a perfect cook every single time.
With such an expensive cut of beef and with your guests drooling over the thought of a great holiday meal, the last thing you want to do is let yourself and everyone else down.
This recipe is simple, effective, and will leave everyone beyond satisfied. Pair the 15 pound prime rib roast with this Horseradish Mustard Cream or a warm au jus and you will have one of the best meals of your life.
What is Reverse Searing?
It seems like every few years there is a new fad or unique way to prepare your food. Reverse searing is one of those techniques that has grown in popularity but it honestly doesn’t matter all that much with a roast this size. If you broiled this roast at the beginning or at the end of the cook on such a large roast you would be hard pressed to notice any difference.
Reverse searing is basically cooking at a low temperature and then searing at the very end instead of the traditional way of searing and then cooking at a lower temperature.
When searing first, it was said that you are locking in the juices of the meat. That actually isn’t true, you are developing outstanding flavor by doing that but you aren’t locking in any juices.
When reverse searing, you cook your beef/protein at a low temp and bring it to the exact temperature you would like. Then you sear it over high heat to develop a crust and flavor.
With over 20 years of experience with cooking beef in professional kitchens, 99 times out 100 I am searing my beef first. I find, contrary to belief that there is far more control in your end internal temperature and the development of flavor is noticeable. To each their own, their isn’t a wrong choice.
Which 15 Pound Prime Rib Roast is the Best?
At most reputable meat markets you are going to find different grades of beef. The most common are select, choice, and prime. Some markets will have a specialty brand that isn’t common that you will need to ask them about. There are so many different companies that promote how their cattle are fed and raised, and some offer some really great beef.
USDA’s highest grade is prime, so don’t be too fooled by fancy brands and labels. With that being said, if you have access to local beef that is raised to the highest standards then you should definitely take advantage of it.
SELECT is the most common found in grocery stores, the cuts usually don’t have great marbling because they are more lean. Select is priced the lowest of the three but you get what you pay for. You can expect your beef to be a bit tough or dry and you will have wished you spent more on the next grade up.
CHOICE is the next grade up from select. It is quality beef that typically has nice marbling and if you search hard enough you will find beef that is comparable to prime without the price tag. This recipe used a choice cut from Costco and it cooked and ate just as a prime cut would.
PRIME is the higher end of beef, it is from younger cattle and it has a ton of marbling. These are the cuts you will eat at a high end restaurant because they don’t have the time or luxury of hand picking through choice cuts to save a few bucks. Prime is consistently perfect and even the worst cuts of prime are equal to the very best cuts of choice. This grade comes with a high price tag so prepare to spend significantly more.
To sum this all up, for this recipe either buy Prime or learn to find Choice beef that has great marbling.
Let's Cook!
This is step by step, exactly what was done on Christmas morning. It doesn’t have to be Christmas morning, it can be any morning but follow these steps and you will get the end product you are looking for.
10am– Remove the 15 pound prime rib roast from the refrigerator, remove it from its packaging. Generously season the entire roast with kosher salt and fresh cracked black pepper. Remember that the only seasoning you will have on your entire slice of beef will be the crust so it is important to go very heavy on the seasoning. Rub the entire roast down with olive oil.
11am-Preheat your oven to broil or 500 degrees Fahrenheit. Coat your entire 15 pound prime rib roast with Dijon mustard then place the roast on a roasting rack inside of a roasting pan.
11:30am– Place the 15 pound prime rib roast in the oven for 20 minutes to allow the roast to begin to develop a crust.
11:50am– Remove the 15 pound prime rib roast from the oven and immediately drop the oven temperature to 250 degrees. Place a leave-in thermometer (pictured below) into the thickest part of the roast. The best way to ensure your roasts are cooked perfectly is by using a leave-in meat thermometer. They are a great investment for those who want to know exactly what temperature your meat is at throughout the cooking process. Just place the probe into the thickest area and set your thermometer to what temperature you would like the meat to cook to, a timer will alert you when you hit your desired temperature.
Noon– Place the 15 pound prime rib roast back into the oven at 250 degrees.
1:30pm– Drop the oven temperature to 225 degrees, leave the roast in you don’t need to remove it for this drop in temperature. This small drop in temperature is to ensure that you are getting the most even cook from edge to center as possible.
2:20pm– The internal temperature of the 15 pound prime rib roast, according to the leave-in thermometer is 125 degrees Fahrenheit. The roast was removed from the oven. Keep the thermometer on and inserted. Place a layer of aluminum foil over the roast and then cover the aluminum foil with kitchen towels. The foil and the towels will just help to insulate the beef while it rests.
3:30– From the time the 15 pound prime rib roast was pulled from the oven the highest internal temperature the 15 pound prime rib roast reached was 135 and then it began to cool until it reached 124 at 3:30 when it was time to carve/slice it. At this time, remove the towels, foil, and meat thermometer and discard the thyme or rosemary that is probably dry and shriveled by now. Carefully, transfer your roast to a large cutting board and while using a sharp knife cut your 15 pound prime rib roast into thick slices depending on preference.
1/2″-1″ slices or anywhere between will not only look amazing to your guests but it will also provide the best eating experience. Slicing too thin will make it look and feel much cheaper than it was. Only slice as much as you need and then serve immediately.
Rest Your Meat!
45 minutes to an hour of resting time may seem like a lot but a 15 pound prime rib roast needs time to rest. Letting your meat rest allows the muscle fibers to relax and redistribute its juices throughout the rest of the meat. Carving too soon will cause those juices to flood out of the meat which will result in dry meat. Be patient, it will be worth it. This step is as important as the cooking process so regardless of the pressure you are feeling to get food on the table, just chill and walk away. Don’t ruin your roast because the green beans are getting cold.
Great Success!
You just absolutely crushed your 15 pound prime rib roast. From the crispy and flavorful outer crust, to the the tender spinalis (rib cap), to the juicy fatty eye, and all the way to the center of the prime rib you have the perfect color and juiciness from top to bottom. Everyone stood up and did a slow clap and if they didn’t it’s only because they were too full to move. Let us know how it turned out for you in the comment section!
Hope you enjoyed this 15 pound prime rib roast recipe, be sure to check out the rest of the site for so many others by Chef Brian Sirois. There are so many side dishes that pair well with this recipe so be sure to at least swing by the Sides and Sauces section of the website.
15 Pound Prime Rib Roast
Ingredients
- 1 15lb Boneless Prime Rib Roast Make Sure the Meat Has Great Marbling Throughout
- 12 Sprigs Thyme/Rosemary or 6 of each
- 6 tbsp Dijon Mustard
- 3 tbsp Olive Oil
- Salt and Pepper
Instructions
- Remove your roast from the refrigerator for at least one hour before cooking to allow it to approach room temperature.
- Preheat oven to 500 degrees Fahrenheit.
- Generously season your roast with salt and fresh cracked black pepper.
- Rub your entire roast down with olive oil.
- Coat the roast with Dijon mustard on all sides.
- Place sprigs of thyme/rosemary/both over top of the roast.
- Place the roast onto a roasting pan, with a rack insert, into the oven for 30 minutes, allowing the roast to start to form a crust.
- Remove the roast from the oven then set the oven temperature to 250 degrees Fahrenheit.
- Insert a leave-in thermometer into the thickest part of the roast.
- Once the oven is at 250 degrees, place the roast back into the oven and roast for 90 minutes.
- Lower the oven temperature to 225 degrees and cook for another 45 minutes or until the internal temperature of the roast is 125 degrees.
- Remove the roast from the oven and cover with a layer of aluminum foil and then place a dish towel or two overtop.
- Allow the roast to rest for 45 minutes to an hour before slicing.
- Slice your roast into 1/2"-1" slices and serve immediately.