Season the Prime Rib: Rub the prime rib with salt and pepper on all sides. Refrigerate for 24 hours, or at least 3-4 hours if short on time.
Prepare for Cooking: Brush the prime rib with clarified butter or avocado oil, then optionally season with herbes de Provence. Preheat the oven to 250°F (121°C).
Cook the Prime Rib: Place the prime rib in the oven and cook slowly. For a 7-pound rib, it will take approximately 3 to 3.5 hours. Cook until the internal temperature reaches 120°F (49°C) for rare to medium-rare.
Rest the Meat: Remove the prime rib from the oven and let it rest for 45 minutes to an hour, allowing the juices to redistribute.
Final Sear: Increase the oven temperature to 500°F (260°C). Brush the prime rib with butter and return it to the oven for 10 to 15 minutes to achieve a golden brown crust.
Serve: Remove the bones, slice the prime rib to your desired thickness, and serve with horseradish sauce and au jus.