Soak the prunes in the hot tea for 2 hours. Drain, reserving the prunes and discarding the liquid. Trim off the loose fat from the duck legs and render it with 2 tablespoons water. Strain, reserving 2 tablespoons for this dish. Keep the remainder for some other purpose. Score the skin of the duck with the point of a small knife. Wipe off excess moisture. Heat the duck fat in a heavy nonreactive skillet over moderate heat. Add the blanched lardons and fry, turning occasionally, until light brown, about 4 minutes. Remove with a slotted spoon and drain on paper towels. Reserve the drippings in the skillet. Transfer the lardons to a 4-quart flameproof casserole. Add the duck pieces to the reserved drippings in the skillet and cook over moderately high heat, turning occasionally, until well browned, about 10 minutes. Briefly drain the duck on paper towels and add to the lardons in the casserole. Add 2 of the garlic cloves, the salt, pepper, and thyme and toss to mix. Pour off all but 2 tablespoons fat from the skillet. Add the red onion to the skillet and sauté over moderate heat, stirring frequently, until lightly browned, about 5 minutes. Remove the onion with a slotted spoon, drain thoroughly on paper towels, and add to the casserole. Pour off all the fat from skillet; whisk in the vinegar, mustard, and ⅓ cup of the wine. Bring to a boil, scraping up any brown bits clinging to the pan. Reduce to a glaze. Add another ⅓ cup wine and reduce again to develop a stronger, deeper color in the sauce. Pour the deglazing liquid from the skillet, the remaining wine, and the stock into the casserole; heat to boiling. Reduce the heat and simmer, uncovered, for 5 minutes, skimming. Add the carrots. Cover the casserole and simmer over low heat until the duck is tender, about 1½ hours; or cook in a preheated 300°F oven. (This recipe can be prepared up to this step. Cool, cover, and refrigerate.) Cut an X in root end of each small onion. Blanch for 2 minutes. Drain and rinse under cold water until cool enough to handle. Peel the onions, leaving on enough root and stem end so the onion won't fall apart. Combine the onions, butter, sugar, and ½ cup water in a medium skillet. Bring to a simmer over moderate heat and cook, stirring occasionally, until the water has evaporated, about 6 minutes. Reduce the heat to low and continue to cook, shaking the pan occasionally, until the onions are tender and nicely browned, about 8 minutes. About 20 minutes before serving, add the prunes to the ragout and gently reheat. Transfer the duck pieces to a warm platter; surround with the prunes, carrots, and onions. Sprinkle the lardons over the duck; tent loosely with foil. Strain the sauce from the casserole through a fine-mesh sieve into a small saucepan, pressing on the solids with the back of a spoon to extract as much liquid as possible. Skim off any fat from the sauce. Bring to a boil and set the saucepan half on and half off the heat. Cook at a slow boil, skimming, for 10 minutes, or until the liquid is reduced enough to coat a spoon lightly. Spoon the sauce over the duck and vegetables and serve at once with the toasted baguette slices. To save time, defrosted frozen baby onions can be substituted for the fresh here. Skip Step 8 and glaze as directed in Step 9. If substituting Muscovy or Moulard duck legs, please note they need to cook longer, as much as 1 hour.
