Remove the prime rib from the refrigerator 2 to 3 hours before cooking to allow it to come to room temperature for even cooking.

Preheat your oven to 450°F (230°C). In a small bowl, combine softened butter, minced garlic, kosher salt, chopped thyme, rosemary, and black pepper to create the herb butter mixture.

Pat the prime rib dry with paper towels, then rub the entire surface thoroughly with the prepared herb butter to ensure a flavorful crust.

Place the prime rib in an oven-safe roasting pan bone-side down and fat-side up. If you are making the au jus, arrange the quartered onion pieces around the meat; otherwise, omit onions.

Roast in the preheated oven at 450°F (230°C) for 20 minutes to sear and develop a crust. If needed, extend this time to enhance browning. Reduce oven temperature to 325°F (160°C) and continue roasting until the internal temperature reaches 120°F (50°C) for medium-rare, approximately 1 hour 30 minutes, but monitor with a meat thermometer for accuracy.

Remove the roast from the oven and tent loosely with aluminum foil. Allow it to rest for 20 to 30 minutes to let juices redistribute. Remove the twine and bones, then slice into ½-inch thick portions.

After removing excess fat from the roasting pan, return up to ¼ cup of drippings to the pan. Add beef broth and red wine along with any leftover herb bits. Simmer gently for about 15 minutes to reduce the liquid by half. For a thicker sauce, stir in cornstarch or arrowroot slurry and cook until desired consistency is reached.

Strain the sauce to remove onion pieces and any browned bits, then transfer to a serving bowl or drizzle directly over the sliced prime rib.