Store in refrigerator for at least 2 days before use - it will keep for months. Cut the duck into small portions. Rub with the sea salt, place in a bowl, weight it down and leave overnight, saving any extra fat and skin. Place the skin and both fats in a saucepan with 120ml water and cook until the water has evaporated. Remove the skin.
Next day wipe the salt off the meat.
Put the meat in a saucepan and cover with the rendered fat. Remove meat to preserving jars, strain fat and pour over meat to cover. Refrigerate when cool. Store at least 1 month before use - it will keep this way for many months. Soak the beans overnight.