2The following day: Rinse off seasonings, blot very dry, and wrap in pairs in boilable pouches, then use a FoodSaver or professional vacuum packing device to seal airtight. Cover one stovetop burner with a Simmer Mat or heat diffuser. Place the sealed pouches in a deep flameproof ceramic or cast-iron casserole and cover with hot water. Be sure the pouches are completely submerged; if necessary, weight them down. Place the casserole over the mat or heat diffuser set over medium-low heat. Cover the casserole and heat to 180°F (use an instant-read thermometer), then reduce heat to low and allow to simmer at a constant 180°F temperature for at least 8 hours for Moulard, 9 for Muscovy, or 5 to 6 hours for Pekin. (If you have an electric oven, alternatively, you can place the pouches in very hot water in a casserole and cook at 180°F overnight. (Because of the constant water temperature, the flesh won’t cook beyond its stage of “doneness.”)
3The duck is ready when the flesh feels very tender, begins to separate from the bone, and the joint between leg and thigh cracks easily. When you remove the pouches from the casserole, immediately set the pouches in a bowl of ice water to chill until completely cold, about 30 minutes. The fat should congeal. Refrigerate until ready to use, within one week (see Cooks' Notes below).
