In a bowl combine all the marinade ingredients and mix well. Put the chicken inside a freezer plastic bag, add the marinade and seal the bag. Let marinate 24 hours in the fridge, turning occasionally.
Next day, make the stuffing. In a saucepan melt the butter, add the onions and beef mince and cook until onions are browning. Add the chestnuts and walnuts and cook 5 more minutes. Add the chicken stock and bring to a simmer.
Add rice and cook until rice is tender and stock mostly absorbed. Let cool.
Soak the bread in the milk and add to the beef mixture. Season with salt, pepper and nutmeg and mix in the egg. Preheat oven to 180 degrees C.
Drain the chicken from the marinade and stuff with the stuffing. Place on a greased baking sheet and brush with melted butter. Roast for 2 1/2 hours, basting regularly with butter, or until golden brown.