1. Prepare Roast: Let roast stand at room temperature 1 hour.
2. Preheat oven to 450°. Whisk together mustard and next 3 ingredients; reserve 1 Tbsp. mixture. Rub remaining mixture over roast; sprinkle with salt and pepper. Place roast on a lightly greased rack in a roasting pan.
3. Bake at 450° on lower oven rack 45 minutes. Reduce oven temperature to 350°; bake 1 hour and 10 minutes or until a meat thermometer inserted into thickest portion registers 120° to 130° (medium-rare) or 130° to 135° (medium). Let stand 30 minutes; transfer roast to a serving platter, reserving drippings in pan.
4. Meanwhile, prepare Red Wine Mushrooms: Skim fat from reserved drippings; place pan on stove top over 2 burners. Melt butter in pan over medium-high heat, stirring occasionally and moving pan as necessary to prevent hot spots. Add mushrooms; sauté 3 minutes. Add shallots; cook, stirring constantly, 3 to 4 minutes or until tender. Stir in wine; cook, stirring constantly, 2 minutes. Stir in broth; reduce heat to medium, and simmer, stirring constantly, 5 minutes. Stir in reserved 1 Tbsp. mustard mixture. Add salt and pepper to taste. Slice roast, and serve with mushroom mixture.
Ask your butcher: Have the chine bone removed. A thin bone that runs perpendicular to the rib bones, it will get in the way of slicing once the meat is roasted and has rested.
Roast like a pro: Start roasting at 450° for 45 minutes to form the caramelized crust. Then reduce the temperature and finish cooking to keep the inside pink and juicy.
The right temp: 125° for prime rib lovers. Remember: The internal temp on large roasts like this will continue to rise as the roast rests.