fryer chicken (4-5 lbs.), neck and gizzards removed, cut into parts • onion, peeled and cut in half • stalks of celery, cut into large pieces • carrots, cut into large pieces • bay leaves • sprig each of thyme and parsley • kosher salt, to taste • peppercorns • of water or chicken broth • unsalted butter • onion, finely chopped • garlic clove, minced •