Preheat the oven to 150°C (300°F/Gas 2). Rub the chicken generously in chicken fat or butter and season with salt, including the cavity. Fill the cavity with the fresh herbs and bay leaves and truss the chicken with kitchen string. Spread the garlic and leek bulbs in the base of a large, ovenproof casserole with a tight-fitting lid, large enough to accommodate the chicken. Add a layer of washed hay and pour in the chicken stock and cider. Place the chicken on top and cover with the remaining hay. Cover with the lid and cook in the oven for 1–1½ hours or until just pink at the thigh joint. Remove from the oven and rest the chicken for 15 minutes.
Strain the cooking liquid into a small saucepan and place over medium heat. Cook for 15–20 minutes or until reduced by a third, seasoning with salt if necessary.
While the chicken is resting, prepare the chicken fat rice: bring 2 litres (70 fl oz/8 cups) of water to the boil in a large saucepan with the bay leaf and salt. Add the rice and boil for 13 minutes. Strain. In a large frying pan over medium heat, put the chicken fat and green garlic and sweat until soft, but do not allow to colour. Add the rice, stirring to combine and ensuring it is thoroughly coated in chicken fat. Season with salt.