Preheat the oven to 200°C/Fan 180°C/Gas 6. Make the garlic butter by pounding the peeled garlic into a paste with a pinch of salt. Mix together 50g of the butter with the garlic paste, parsley, lemon thyme and lemon zest.
Season the chicken with salt and pepper. Place on a rack in a roasting pan. Place the unpeeled garlic clove and the squeezed lemon half inside the chicken cavity. Pour over the lemon juice.
Using your fingers, gently pull the skin away from the chicken breast. Insert the garlic butter under the skin and on to the flesh, pressing down to spread it evenly over the chicken breast. Dot the remaining butter over the chicken legs and wings
Roast the chicken in the preheated oven for 1 hour 20 minutes–1 hour 30 minutes, basting often with butter juices, until cooked through and the juices run clear. Rest for 15 minutes.
Meanwhile, use the roasting juices to make a gravy. Skim off excess fat from the roasting juices. Heat the oil in a pan, add the onion and bay leaf and fry gently until the onion has softened. Add the wine, cook briefly, then add the stock and the roasting juices. Bring to a boil and cook until slightly reduced. Season as required. Discard the bay leaf and serve at once with the chicken.