Preheat your oven to 325 F.
Combine the tallow or butter with the horseradish, garlic, sage, thyme and rosemary in a food processor and process to a smooth purée.
8 cloves garlic, 1 cup prepared horseradish, ¼ cup + 2 tablespoon fresh thyme leaves, 3 tablespoon fresh rosemary leaves, 3 tablespoon fresh sage, ½ lb beef tallow
Place the roast, fat side up, in a roasting pan, season with sea salt and freshly ground black pepper, and then and rub the horseradish and herb purée all over it. Add chicken broth to base of pan.
16 lb bone-in prime rib roast, Sea salt and freshly ground black pepper, 2 cups chicken stock
Place in the oven. For a medium-rare roast, cook for about 3 ½ hours, until it reaches a temperature of about 3 ½ hours, until it reaches a temperature of 125 F in the center of the roast. Refer to the cooking times chart if your roast has a different weight.
Baste the roast occasionally during the cooking process. When cooked, remove the roast from the oven and set aside to cool for at least 20 minutes before carving and serving