How to Make It
Season the meat with salt and pepper. In a large enameled cast-iron casserole, heat 1 tablespoon of the vegetable oil until it is shimmering. Add half of the beef and cook over moderately high heat until the meat is browned all over, about 12 minutes. Transfer the meat to a large, shallow bowl. Repeat with the remaining vegetable oil and meat.
Add the garlic and onion to the casserole and cook over low heat, stirring occasionally, until softened, about 8 minutes. Return the meat and any accumulated juices to the casserole. Add the wine and bring to a boil, then reduce the heat and simmer for 2 minutes. Add the thyme, tomatoes, carrots, bay leaf, spice bag and stock and bring to a boil. Cover partially and simmer over low heat until the meat is tender, about 1 1/2 hours. Let cool, then refrigerate overnight.
Cover the stew and rewarm it over low heat. Meanwhile, melt the butter in a large skillet. Add the quartered mushrooms, season with salt and pepper and cook over moderately low heat until they release their liquid, about 6 minutes. Pour 2 tablespoons of the liquid into a small bowl and let cool. Cook the mushrooms over moderate heat, stirring occasionally, until they are browned, about 6 minutes longer. Add the mushrooms to the stew.
Return the large skillet to moderate heat. Add the water and turnips and season with salt. Cover the skillet and cook the turnips over moderate heat until they are just fork-tender, about 5 minutes. Add the turnips to the stew. Discard the thyme sprigs, bay leaf and the spice bag.
Whisk the flour into the reserved mushroom liquid to form a paste. When the stew comes to a simmer, stir 1/2 cup of the sauce into the paste until blended. Stir the paste into the stew and bring to a boil. Simmer the stew over moderate heat, stirring frequently, until the sauce thickens, about 2 minutes. Season the stew with salt and pepper, stir in the parsley and serve.
Make Ahead: The beef stew can be covered and refrigerated for up to 2 days. Bring the stew to room temperature and reheat gently before serving.
Serve With: Buttered noodles.