Preheat the oven to 160*/300*F/ gas mark 3.  Lay the chicken legs in a single layer in a baking large enough to fit them.  Rub them all over with the softened butter.  Sprinkle the lemon zest over all, aong with the black pepper, parsley flakes and sea salt to taste.  Squeeze the lemon juice over top. Cover the dish tightly with foil and bake them in the preheated oven for 1 hour.  Increase the oven temperature to 225*C/425*F/ gas mark 7.  Remove the foil and baste the chicken legs with the pan juices.  Continue to cook for a further 15 to 20 minutes, or until the chicken is golden brown and the juices run perfectly clear.  Serve hot.