Garlic-Shallot Crust

1. Make the roasted garlic-shallot purée: Preheat the oven to 375°F. Place the garlic cloves and shallot halves on a small sheet of foil. Drizzle with olive oil and season lightly with salt and pepper. Wrap loosely and roast for 45 minutes, until caramelized and tender. Squeeze the garlic and shallot flesh into a small bowl, mash into a smooth purée, and cool completely.

Prepare and Roast

1. Prepare the roast: Remove the prime rib from the refrigerator while you prepare the crust, no more than 30 minutes before roasting. Pat it thoroughly dry with paper towels. Place the roast fat-side up on a rack fitted inside a large roasting pan.
2. Apply the crust: Coat the top and sides evenly with the cooled garlic-shallot purée. Season on all sides with fleur de sel and cracked black pepper. Roast once the crust is applied.
3. Roast: Increase the oven temperature to 450°F. Place the roast in the oven and immediately reduce the temperature to 325°F. Roast uncovered until a thermometer inserted into the thickest part reaches 145°F. Begin checking after about 1 1/2 hours; a 5 to 6 lb roast may take about 1 3/4 to 2 1/2 hours. Oven time varies, so use the thermometer.
4. Rest: Transfer the roast to a carving board and tent loosely with foil. Rest for 25 to 30 minutes. Rest at least 3 minutes for food safety; the longer rest helps keep the juices in the meat.

Pan Jus and Serving

1. Make the pan jus: Place the roasting pan over medium-high heat. Add the beef stock or water and scrape up the browned bits. Simmer for 2 minutes, season to taste, and strain into a warm sauceboat.
2. Carve and serve: Slice the roast across the grain into thick, even slices. Serve with warm pan jus and fleur de sel at the table.