Grind pepper over roast; press into meat. Mix tamari, Worcestershire sauce and dry mustard. Spread mixture over roast. Pack sliced onion on roast; hold in place with toothpicks, if needed. Place roast on rack in roasting pan. Roast at 450°F for 20 min. Reduce oven temperature to 325°F and roast 20 min. Reduce heat to 300°F and roast 20 min. more or until beef registers 115°F for rare in the center. Remove from oven, allow to stand 15 min. Slice and serve with Wine Gravy.
Bring beef stock and wine to boil in saucepan. Simmer, uncovered, until reduced to 2 cups. Add any pan drippings from rib roast, stir. Melt butter; stir flour into butter and cook 1 minute, or until bubbly. Add roux to broth, cooking and stirring until thickened. Add broth or water, as needed to reach desired consistency.