Melt 5 tablespoons of the butter in a medium saucepan over low heat. Add the shallots and cook over medium-low heat, stirring occasionally, until soft and translucent, 7 to 8 minutes. Add the wine, beef broth, thyme sprigs, salt, pepper and sugar, and bring to a boil. Cook over medium heat for about 30 minutes, until the liquid is reduced by about half.

While the liquid is reducing, place the remaining 3 tablespoons of butter in a small bowl and soften in the microwave, if necessary (it should be soft but not melted). Add the flour and, using a small spoon, mix into a smooth paste.

Once the wine mixture is reduced, reduce the heat to low and remove the thyme sprigs. Whisk the flour-butter paste, a teaspoonful at a time, into the simmering liquid, and simmer for a few minutes, until the sauce is thickened. Set aside. (The sauce can be made up to this point and refrigerated up to 3 days ahead of time.)

1 hour before roasting, pull the meat from the fridge to take some of the chill off. Pat it really dry with paper towels. Oil the meat with 2 ½ Tablespoons of olive oil and season it well with salt and pepper. Tie a couple pieces of twine around the tenderloin, spacing them out 2-inches apart. Secure the rosemary sprigs to the meat by threading them through the twine. Brush the rosemary sprigs with the remaining ½ tablespoon of olive oil. Line a baking sheet with foil for easy cleanup, if desired. Place a metal rack over the baking sheet and place the meat on the rack.

Preheat the oven to 275 F degrees and position a rack in the center.

Place baking sheet with rack and tenderloin in oven and roast until internal temperature registers 120 to 125 F for rare on an instant-read thermometer, about 1 to 1 ½ hours. Remove from the oven and set aside at room temperature for 10 minutes. Cut and remove twine.

OPTIONAL: To Finish Under the Broiler: Adjust rack to 6 inches from broiler element and preheat broiler to high. Place pan with tenderloin under broiler and broil, turning every 30 seconds, until meat is well browned on all sides and internal temperature registers 125 F for rare or 130 F for medium-rare, about 2 minutes total.

Transfer the roast to a carving board (preferably with grooves for collecting juices) and let it rest, covered loosely with aluminum foil, for 10 minutes. This allows the juices to redistribute from the outside of the roast throughout the whole roast, making the tenderloin juicy. If you slice it too soon, the juices will pour out of it.

Reheat the sauce. Transfer the meat to a warmed platter and pour the juices from the cutting board into the sauce. Slice tenderloin into rounds and serve with wine sauce.