Preheat oven to 425F/220C.
Using kitchen scissors cut along both sides of the backbone and remove it. Trim skin and remove excess fat.
Press down on the breastbone to flatten the chicken.
Zest lemon, slice lemons and place in casserole. Top with bay leaves and rosemary.
Combine parsley, lemon zest and garlic. Tuck under skin on one side of breast.
Brush butter on both sides of chicken and season with salt and pepper. Tuck wings under breasts and place in metal baking dish.
Roast in oven for 45 minutes, or until golden brown and juices run clear and internal temperature reaches 170F/80C.
Remove from oven and tent with foil for 10 minutes. Cut 2 leg and 4 breast portions.