Preheat your oven to 450°F (232°C). In a small bowl, combine the cracked allspice, kosher salt, and black pepper. Rub the mixture all over the prime rib roast.

In a large oven-safe skillet or roasting pan, heat the olive oil over medium-high heat. Sear the prime rib on all sides until browned, about 3-4 minutes per side.

Once the prime rib is seared, remove it from the pan and set it aside. In the same pan, add the halved leeks, cut side down. Cook until they are charred, about 4-5 minutes. Turn them over and cook for another 2-3 minutes, just to soften slightly.

Place the prime rib back in the pan, on top of the charred leeks. Insert a meat thermometer into the center of the roast. Roast in the preheated oven for 15 minutes, then reduce the temperature to 325°F (163°C) and continue to roast until the internal temperature reaches your desired doneness (about 130°F (54°C) for medium-rare), roughly 1.5 to 2 hours depending on the size of the roast.

While the roast is cooking, prepare the gravy. In a saucepan, combine the roasted garlic (squeeze the cloves out of the bulb), beef stock, and red wine. Bring to a simmer over medium heat and let it reduce by half, about 15-20 minutes.

Once reduced, whisk in the butter until melted and smooth. Season with salt and pepper to taste.

Once the prime rib is done, remove it from the oven and let it rest for at least 20 minutes before slicing. This helps retain the juices.

Serve slices of prime rib with charred leeks on the side, drizzled with the roasted garlic gravy. Garnish with fresh thyme sprigs.