If time allows, set your completely thawed prime rib roast to warm to room temperature (about 1 to two hours) for faster and more even cooking.
Preheat your oven to 450 degrees F (232 degrees C) and move oven racks if necessary, to position your roast in the center of the oven.
In a small bowl, combine roasted garlic, horseradish, Worcestershire sauce, and lemon juice until blended. Rinse and pat dry your rib roast, then coat your entire prime rib roast with the horseradish roasted garlic sauce, then set into a shallow roasting pan or dish, preferably on a rack (or the cut away rib roast bones) with the fat layer facing upward.
Sear the roast for the first 15 minutes of cooking at 450 degrees F (232 degrees C), then reduce the temperature to 325 degrees F (162 degrees C) and continue to cook your roast for an additional 45 minutes.
When the internal temperature (inserted into the thickest middle portion of the roast) reaches 120 degrees F (49 degrees C), remove the roast from the oven and transfer to a cutting board. Then cover loosely with aluminum foil, forming a ‘tent’ over the roast while allowing your prime rib to rest for 20-30 minutes before serving. The internal temperature should be 130 degrees F (54 degrees C) when the roast has rested, before serving.
*Remember that cooking times will vary depending on your oven temperatures and the size of your prime rib portion, rely on your meat thermometer for removing the roast at an internal temperature of 120 ºF (49 ºC) and 130 ºF (54 ºC) when done resting.**Cooking times are approximately 12-15 minutes per pound after the initial 15 minute sear of your roast. If you are using a larger roast, follow instructions as above, but extend the cooking time after reducing the oven temperature (ie. I would temp an 8 pound roast at about 1 hour 15 minutes, and a larger 12 pound roast at about 2 hours 20 minutes).**Save your pan juices for making my traditional Yorkshire puddings with the fat, and my prime rib red wine au jus with the strained beef juices!