Procedure:
Two hours before cooking, remove meat from refrigerator and set on a countertop to bring to room temperature. Preheat the oven. Combine flour, dry mustard and onion powder and pat onto roast. Season generously with salt and pepper. Place roast in large roasting pan, bone side down, add the onion. Roast meat for approximately 1 hour total.
Remove roast from oven to platter. When ready to serve, transfer to a cutting board and carve into thick slices. Now prepare the gravy. Remove onions and but 3 Tbsp. of fat from roasting pan. Place pan on medium heat, sprinkle in flour and cook, whisking constantly, for 2 minutes.
Add wine and broth and bring to a boil. Reduce heat and simmer until gravy reaches desired consistency. Season gravy with salt and pepper and add any juices that accumulated on platter while meat was resting. Strain gravy and serve with roast.