Preheat the oven to 230°C (210°C fan) and place an oiled rack inside a roasting dish. Toast the bread on an oven rack until crisp. Cut into 1cm cubes and transfer to a large bowl. Cook pancetta for about 5 minutes in a large, deep frying pan over moderate heat until crisp. Remove with a slotted spoon, drain on paper towels and add to the bread.

Add onion to the frying pan and cook for about 5 minutes, until soft, stirring frequently. Add garlic and stir for a further 1 minute. Stir in the silverbeet and thyme and cook until silverbeet has wilted. Transfer to the bread mix.

Add 300ml chicken stock to the pan. Bring to a boil over high heat. Add the bread mix to the stock and let stand for 10 minutes to absorb. Spoon into a lightly greased ovenproof dish.

Brush chicken with oil and season to taste. Place in the prepared roasting dish and roast for 30 minutes, until skin is light golden. Add potatoes to the pan, season and scatter with thyme sprigs, then roast for a further hour, until chicken is golden brown and juices run clear when a thigh is pierced. Add halved garlic bulbs for the last 30 minutes. Bake the bread mix for 30 minutes, until the top is golden and crisp. Transfer chicken and potatoes to a heated platter.

Pour off all the fat in the roasting dish and add the extra cup of chicken stock. Bring to a boil, scraping up any browned bits, and boil for about 5 minutes, until the liquid is reduced and slightly thickened. Check seasoning and pour into a sauce boat. Carve the chicken into serving pieces and serve with the stuffing and gravy.

Note: the stuffing is cooked separately in this recipe so it develops a golden crust rather than becoming soggy inside the bird.