Perfect Prime Rib Roast

• 3kg Prime rib roast
• 1 tablespoon kosher salt

For the horseradish cream sauce (optional):

• 1 cup heavy cream
• 1 cup sour cream
• 1/4 cup prepared horseradish
• 1 teaspoon freshly ground black pepper
• 1/2 teaspoon kosher salt
• 1/4 teaspoon cayenne pepper (optional)

Method

1. Pat the standing rib roast dry with paper towels and season generously with 1 tablespoon kosher salt, being sure to coat the sides, ends, and the ribs below. Don’t worry about using all the salt. Place the roast in a roasting pan or metal baking pan with the ribs in the pan and the fat cap up. Let sit at room temperature for about 2 hours.
2. For the horseradish sauce, place 1 cup heavy cream, 1 cup sour cream, 1/4 cup prepared horseradish, 1 teaspoon freshly ground black pepper, 1/2 teaspoon kosher salt, and 1/4 teaspoon cayenne pepper (optional) in a medium bowl. Whisk until smooth. Cover and refrigerate until ready to serve.
3. Arrange a rack in the middle of the oven and heat the oven to 260°C.
4. Place the roast in the oven for 15 minutes. Be prepared — during this time, the roast is going to put off a fair amount of fat and there will be smoke. Turn on your stove or oven’s vent and open a few windows. Don’t worry, the roast will be done with smoking after this and your kitchen will be smoke-free long before guests arrive for dinner.
5. Drop the oven temperature to 180°C and continue to cook the roast for at least another hour before you begin checking the roast’s temperature. Larger roasts can take a total of 1 1/2 to 2 hours. Roast until the center of the prime rib registers 50°C for rare and 60°C for medium on a instant-read thermometer — remember that there will be carryover cooking as the roast rests.
6. When the roast has reached your desired temperature, remove the roast from the oven and transfer to a clean cutting board for carving. Loosely cover in aluminum foil and let rest for 30 minutes.
7. Cut off the twine or cut the meat away from the bones in one piece. Cut crosswise into 3cm-thick slices. Serve with plenty of horseradish cream or gravy.

Source:  https://www.thekitchn.com/how-to-make-classic-prime-rib-the-simplest-easiest-method-252041