Rinse the bird. Liberally salt and pepper the inside of the chicken. Stuff the cavity with a large bunch of thyme, a lemon cut in half and a whole head of garlic cut cross ways. Brush the outside of the chicken with butter and then sprinkle outside with salt and pepper. Tie legs together with kitchen string and tuck wing tips under body. Place onions (1 large cut in big chunks), carrots (4 carrots cut in 2 inch chunks, and a bulb of fennel (top removed) in a roasting pan, toss with salt and pepper and 20 sprigs of fresh thyme and olive oil. Spread around a roasting pan and place chicken on top. Roast for 1.5 hours or when juices run clear when you cut between leg and thigh. Remove the Chicken and veggies to a platter and cover with aluminum foil for about 20 minutes. Serve.