Using the flat side of a knife, mash 4 cloves garlic with 1 tablespoon salt until the mixture forms a paste. Mix in the chopped rosemary, 2 teaspoons pepper and the paprika.
Coat the roast with the garlic mixture and transfer fat side up to a roasting pan. Cover with plastic wrap and let stand at room temperature for 2 hours (or refrigerate overnight, then let stand at room temperature for 1 hour before roasting). Remove the plastic wrap before roasting.
Position a rack in the center of the oven and preheat to 450 degrees . Transfer the roasting pan and meat to the oven and cook for 20 minutes. Lower the temperature to 350 degrees and continue cooking for 1 hour. Brush the roast all over with 3 tablespoons mustard and roast until it reaches 115 degrees on an instant-read thermometer for rare, about 30 minutes more (the temperature will continue to rise). Transfer to a carving board with a well, tent loosely with foil and let the meat rest for 20 to 25 minutes.
Meanwhile, discard the fat in the roasting pan, leaving the drippings. Place the pan over medium-high heat, add the brandy and simmer for 3 minutes, scraping up any browned bits at the bottom of the pan. Add the beef broth and rosemary sprig. Smash the remaining garlic clove and add to the pan. Simmer for 10 minutes. Whisk in the remaining 1 tablespoon mustard; strain.
Carve the roast, adding any carving juices to the mustard sauce.