Preheat oven to 375°F Season roast with salt and pepper.
In a small bowl, combine garlic, mustard, mayonnaise and horseradish. In another small bowl, combine parsley, thyme, dill and 1 tablespoon of mustard mixture.
Place the beef, rib-bone down, in a roasting pan; coat top with remaining mustard mixture and cook meat until an instant-read thermometer inserted in center of roast registers 110°F Coat roast with remaining mustard mixture and press herb mixture onto mustard with your hands.
Continue cooking roast until a thermometer inserted into the center of the beef registers 140°F for medium, or longer until desired degree of doneness.
Cover loosely with foil, and let the beef stand 20 to 30 minutes before carving into 12 thick slices. Yields 1 slice per serving.