Bring to Room Temperature: Remove the prime rib from the refrigerator 2 to 3 hours before cooking. The meat must be at room temperature for this cooking method to work properly.
Preheat the Oven: Preheat your oven to 550°F (or the highest temperature your oven reaches, typically 500°F).
Prepare the Roast: Use paper towels to pat the entire roast completely dry.
Season the Meat: In a small bowl, mix together the kosher salt, black pepper, and garlic powder. Rub this mixture generously all over the top, sides, and bottom of the prime rib.
Place in Pan: Place the seasoned meat into a shallow roasting pan, fat side facing up. (If using a bone-in roast, the bones will act as your rack. If using boneless, place it on a roasting rack).
Calculate Cooking Time: Weigh your roast exactly. Multiply the weight by your desired doneness:
For RARE: Multiply weight by 5 minutes.
For MEDIUM: Multiply weight by 6 minutes.
For WELL DONE: Multiply weight by 7 minutes.
(Example: A 6 lb roast for Medium doneness = 6 x 6 = 36 minutes).
Searing Phase: Roast the prime rib uncovered at 550°F for the exact time you calculated in Step 6.
The Closed-Door Phase: When the timer goes off, turn the oven completely off. DO NOT OPEN THE OVEN DOOR. Leave the roast in the turned-off oven for exactly 2 hours.
Slice and Serve: After 2 hours, remove the meat from the oven. Because it has rested in the cooling oven, it is ready to slice and serve immediately. Enjoy your perfectly cooked prime rib!