7. Seal with fat
Vacuum seal the legs with 2 tbsp of duck fat per leg. You may seal the legs together into a single bag, but ensure there’s enough room that they don’t touch. By sealing the legs before cooking, we ensure that the fat, juices, and flavor they release will stay in the bag, rather than waft into the air. We add duck fat (or butter, if rendered duck fat is unavailable) to fill in the nooks and crannies around the duck as the bag relaxes in the heat of the oven.