1. Preheat oven to 400 degrees. Place potatoes (and turnips, if using) in a large roasting pan, and toss with 3 tablespoons olive oil. Season with 2 teaspoons salt and 1/4 teaspoon pepper. Roast until golden brown and crisp, 30 to 40 minutes. Remove pan from oven; set aside. Reduce oven temperature to 350 degrees.

2. Lay parsley, thyme, and bay leaf on a piece of cheesecloth. Bundle and tie with kitchen twine; set aside. Cut leeks in half lengthwise, making sure not to cut through the root. Rinse well under cold running water to remove any dirt. Cut the leeks crosswise into 1-inch half moons; set aside.

3. Combine flour, remaining teaspoon salt and 1/2 teaspoon pepper, paprika, and allspice in a small bowl. Place beef on a work surface, and pat dry with paper towels. Sprinkle flour mixture over meat, and pat to coat well.

4. Heat remaining 2 tablespoons olive oil in large Dutch oven (about 7 quarts) over medium heat until hot, but not smoking. Sear roast on all sides until golden brown, about 2 minutes per side. Transfer to a plate; set aside.

5. Reduce heat to medium-low. Add leeks and garlic, and cook, stirring occasionally, until leeks are just softened, about 3 minutes. Add wine, and deglaze pan, scraping up any browned bits from the bottom of the pan with a wooden spoon. Bring to a boil; cook until most of the wine has evaporated. Add beef stock, tomato paste, bouquet garni, and reserved roast. Cover, and place in oven for 30 minutes. Turn the roast over, and cook for 30 minutes more.

6. Add carrots, cover, and return to oven for 1 1/2 hours, turning the roast over every 30 minutes.

7. Add roasted potatoes and turnips to pan, submerging them halfway in the liquid. (This leaves the vegetables tender and crisp.) Place in oven, uncovered, for 30 minutes more to let some of the liquid evaporate. Season with salt and pepper, if desired.

8. Transfer meat to a cutting board to rest for 5 minutes. Discard string, and slice meat. Serve with vegetables and sauce on the side.