A day before you are planning to cook your prime rib, place a wire rack on a sheet pan. Place the meat on top and dry it on all sides using paper towels. Sprinkle 2 tablespoons of kosher salt over the entire rib roast, firmly pressing to adhere.
Place it in the fridge, uncovered, overnight, or for up to 48 hours.
Two hours prior to roasting, remove your prime rib from the fridge and let it come to room temperature.
Meanwhile, prepare the prime rib seasoning by mixing together the black pepper, rosemary, thyme, and garlic powder in a small bowl. Mix until fully combined.
Preheat the oven to 250 degrees F (121°C)
Dry the prime rib thoroughly with paper towels on all sides. Rub it with the prepared seasoning mixture on all sides, pressing down firmly to ensure that it adheres to the meat. Ensure that the meat is on the wire rack with the fat side (aka fat cap) up.
Slow roast the beef in the oven for 3 to 3 ½ hours until it reaches your desired doneness. It is best to use a meat thermometer (*please read the note below for more information) for foolproof results. We recommend cooking it until it reaches 115 degrees F (46 °C) for medium rare. Keep in mind that it will continue to cook after you remove it from the oven with the help of carry-over cooking.
Remove the standing rib roast from the oven, tent it loosely with foil, and let it rest for 30 minutes (and no more than 45 minutes) on the counter.
While the meat is resting, turn the oven temperature up to 550 degrees F. (288 °C) If preferred, make prime rib au jus while the prime rib is resting.
Transfer the meat to the now-preheated oven and let it roast for 5 minutes or until a nice crust is formed. We recommend keeping a close eye on it during this time to avoid burning the crust of the meat.
Once the cooking time is completed, you can enjoy it right away. There is no need to let it rest. To carve, cut the meat off the bone using a serrated (or a very sharp) knife, following the curve of the rib and slicing against the grain to your desired thickness. Serve.