For the turkey leg, first de-bone and de-sin the lower leg using a knife and biting forceps. To do this, simply run a pointed knife along the bone and loosen the meat from the bone. Then pull the tendons and cut them off with the knife.
Using a blender, finely puree the rosemary, thyme, soy sauce, Maggi sauce, teriyaki sauce, Worcester sauce, oil, lemon juice, salt and pepper. Place the drumstick in a freezer bag and add the seasoning sauce and marinate, sealed, in the refrigerator overnight.
Place the spiced turkey leg together with the marinade in a roasting pan, pour the water and the soup powder over it and roast at 170 °C for about 1 1/2 hours. After 3/4 hour, add the potato to the roast.