Pat the prime rib roast dry with paper towels. Sprinkle all sides evenly with kosher salt and press the salt gently into the meat. Cover the roast loosely with foil and refrigerate to dry brine. Allow it to brine as long as possible, up to 48 hours, but even a few hours is beneficial. If short on time, salt the meat and let it dry brine while coming to room temperature in the next step.

Remove the dry-brined prime rib from the refrigerator and let it sit at room temperature for 4-5 hours (for a 10 lb roast), or 3 hours for a smaller one. Meanwhile, preheat your oven to 500°F and ensure the rack is in the lower third. As the roast rests, arrange the quartered onion, halved garlic head, 5 sprigs of thyme, and 3 sprigs of rosemary in the bottom of a nonstick roasting pan to create a flavorful roasting bed.

Crush the mixed whole peppercorns by placing them in a plastic bag and using a rolling pin. Transfer the crushed peppercorns to a medium bowl. Add olive oil, finely chopped fresh rosemary, minced fresh thyme, chopped garlic, onion powder, paprika, ground coriander, and dry mustard. Stir thoroughly to combine into a fragrant, coarse paste.

Lightly pat the room-temperature prime rib dry with paper towels. Rub the entire surface of the roast with the prepared garlic herb pepper spice rub from Step 3, making sure all sides are evenly coated. Place the roast bone-side down and fat-side up on top of the vegetable and herb roasting bed in the roasting pan. Insert a digital meat thermometer into the center thickest part of the meat. Roast, uncovered, at 500°F for 20 minutes to sear the exterior.

After searing, take the roasting pan out of the oven and lower the oven temperature to 250°F. Dot the top of the roast with cubed unsalted butter, spacing the pieces evenly across the surface. Return the roast to the oven and continue roasting, uncovered, at 250°F until the thermometer registers 122°F for medium-rare (the temperature will rise to around 129°F as it rests). This takes about 15 minutes per pound, but I always trust my digital thermometer over the timing for perfect results.

Remove the roast from the oven and generously baste it with the pan juices. Transfer the prime rib to a cutting board, cover loosely with foil, and let it rest for at least 20 minutes. This allows the juices to redistribute and the temperature to reach your desired doneness. Remove the string, unwrap the roast, and separate the bones. Lay the roast flat and carve into 1/2-inch thick slices, or to your preference. I always let my prime rib rest because it keeps each slice so juicy.

Arrange the carved prime rib on a serving platter and serve alongside horseradish sauce or your preferred accompaniments such as au jus or red wine sauce. For an extra kick, I love offering homemade horseradish sauce—it’s a classic pairing!