Roast: Place beef, bone side down, on greased rack in roasting pan. Brush top and sides of beef with mustard. Stir together rosemary, thyme, peppercorns, garlic, orange zest and salt; spread over beef, pressing to adhere. (Make-ahead: Cover and refrigerate for up to 24 hours.)
Roast in 450°F oven for 19 minutes. Reduce heat to 275°F; roast, basting occasionally if necessary, until instant-read thermometer inserted in centre reads 140°F for medium-rare, 2 ½ to 3 ¼ hours. Transfer to cutting board; let rest for 15 minutes before slicing across the grain.
Gravy: While beef is resting, discard all but ¼ cup of fat from pan. Sprinkle in flour; cook over medium heat, stirring, until fragrant and golden, about 3 minutes. Pour in wine; cook, whisking, until thickened, about 1 minute. Add broth, orange juice, mustard, salt and pepper; cook, whisking, until thickened, about 5 minutes. Stir in additional broth or water if necessary, to reach desired consistency. Strain through fine-mesh sieve into serving bowl.
Top beef with gravy and serve with 2016 Cabernet Franc, St. David’s Bench Vineyard.