Place the hen legs in an oven proof dish just big enough to fit the legs sprinkle with a generous amount of sea salt, cover and refrigerate over night. (If the dish is to big, you will need a much larger quantity of fat to cover the legs.)
Pour over duck fat so that the legs are covered. Bake in the oven at 245°F (120°C) for 4 hours. Cool down. The confit keeps for 2 weeks in refrigerator.
To serve, bake the legs in the oven at 350°F (180°C) for 6 to 8 minutes, or until golden brown. Serve with green salad and mustard.