02Preheat oven to 350 degrees.03Add the remaining oil to the pan, lower the heat and saute the onion, leeks and celery until they are soft and lightly browned. Stir in all but one-half teaspoon of the garlic, then add the wine. Simmer for a few minutes, scraping the browned particles from the bottom of the pan.04Stir in the rosemary, parsley sprigs and bay leaves. Season the mixture with salt and pepper, then return the lamb to the pan. Cover and place in the oven to bake until the lamb is very tender, about three hours.05While the lamb is baking, mix the remaining garlic with the minced parsley and lemon peel and set aside.06When the lamb is tender, remove it from the pan. Bring the liquid to a simmer on top of the stove and taste it for seasoning, adding more salt and pepper if necessary. Dissolve the potato starch or cornstarch in the cold water and stir it in to thicken the sauce, then stir in the lemon juice. Return the lamb to the pan and baste it with the sauce. Keep warm until ready to serve or, if desired, prepare it in advance and reheat it just before serving.07Transfer the lamb to a platter and spoon the sauce over it. Sprinkle with the chopped parsley, garlic and lemon peel mixture and serve.