Place the roast bone-side down on a rack in a large roasting pan
Season roast all over with salt and pepper and 'massage in'
Thoroughly combine Dijon mustard and thyme leaves in a small bowl
Brush the mustard/thyme mixture over the meat (do not coat the bottom)
Allow roast to stand uncovered for 2 hours to come to room temperature
Preheat oven to 350ºF
Place the roast in the center of the oven and allow to roast (uncovered) until a meat thermometer inserted into the center of the meat reads 120ºF (apx 1 hour 15 minutes - 2 hours)
Remove from oven and transfer the roast to a carving board and loosely cover with foil - Allow to rest for 45 minutes before carving
Make the Gravy:
(Choose the method that works for you)
Method 1:
Place the roasting pan over 2 burners on the stove top set to medium-high and bring to a simmer - Whisk in the flour until thoroughly combined - Whisk in the beef broth - Return to a simmer (stirring constantly)
Reduce heat to medium-low and continue to simmer (stirring regularly) for 5-7 minutes until thickened - Adjust seasoning with salt and fresh ground pepper to taste
Method 2:
Transfer the drippings from the roasting pan to a large, wide sauce pan - Add 1 cup of the beef broth to the roasting pan and use a rubber/silicone spatula to gently scrape up any 'browned bits' from the bottom of the roasting pan - transfer to the sauce pan
Place over medium-high heat and bring to a simmer
Whisk in the flour until thoroughly combined - Whisk in the remaining beef broth and return to a simmer (stirring constantly)
Reduce heat to medium-low and continue to simmer (stirring regularly) for 5-7 minutes until thickened - Adjust seasoning with salt and fresh ground pepper to taste
Serve carved roast with hot gravy along with any sides you prefer - Yorkshire pudding, crispy roast potatoes ('roasties), honey roasted parsnips, pigs in blankets, brussels sprouts, parsnip mash, etc...