Put the chicken and its giblets in a large pot or pan, together with the onions, celery, carrot and bouquet garni. Add enough water to cover the legs if it is a roasting bird, or to cover it completely if a boiling fowl. Bring to simmering point and skim. Adjust the heat to maintain a low simmer, 190°F/90°C, and cover. A roasting chicken will need an hour or so, a boiler anything over 2 hours.