Preheat the oven to 220°C. In a small frying-pan sauté the onion and celery in the butter until softened. Combine in a large mixing bowl with the bread, pepper, eggs, Manchego, salt and sage.
Pack the cavity of the chicken with the stuffing. Season the skin with salt and pepper, then tie the legs together with butcher’s string. Place in a greased and lidded shallow casserole, cover and roast for about 2 hours. Take the lid off for the last 15 minutes to brown.
Remove from the oven. Allow to rest for 10–15 minutes, then carve on a large platter and serve.
Manchego cheese is made from the milk of Manchego sheep and is aged for three months or longer. It has a rich golden colour and melts beautifully when cooked. Try cubes of Manchego cheese with fresh pear or with quince paste. Pack cubes of Manchego loosely into a jar and cover with extra virgin olive oil, adding dried herbs such as wild thyme or a little rosemary or even chilli if you like spicy flavours. Seal and leave for a minimum of 1 month before eating. The cheese will continue to mature for up to a year.