How to Make It
In a bowl, mix the salt with the crushed peppercorns and the thyme. Put the duck legs in a large, shallow container and sprinkle them all over with the seasoning mixture. Cover and refrigerate overnight.
Rinse the legs and dry them thoroughly with paper towels. Using a vacuum sealer, package and seal the legs in pairs.
Set a large, enameled cast-iron casserole over a heat diffuser on the stove. Add the pouches and enough hot water to cover generously. Top the pouches with a heatproof plate to keep them submerged. Cover the casserole and bring the water to 180° over moderately low heat. Reduce the heat to low and cook at 180° for 5 hours. The duck legs are ready when they feel very tender and the meat begins to separate from the bone. The joints between the legs and thighs should crack easily when pressed firmly.
Prepare an ice water bath. With tongs, transfer the pouches to the water bath and let soak until the duck legs are cold and the fat has solidified. Dry off the pouches and refrigerate for up to 1 week. If a refrigerated pouch begins to puff up, discard it.
To serve, open the pouches and scrape the fat off the legs. Roast or pan-fry the confit until warmed through and crisp.