1 Rinse chicken and pat dry. Remove the backbone with poultry shears.
2 Place chicken skin side down on the work surface, pressing firmly to flatten. Place in a shallow dish.
3 Rinse rosemary and shake dry. Remove needles from stem; discard stem. Peel the garlic. Chop both rosemary needles and garlic together.
4 Mix rosemary and garlic with olive oil, salt and pepper and spread on the chicken, placing some of the mixture under the skin. Refrigerate chicken at least 1 hour, preferably marinate the chicken overnight in the refrigerator.
5 Place the chicken with skin side down in a heavy, large ovenproof pan or roasting pan. Wrap a brick in aluminum foil and weight down the chicken with the wrapped brick. Brown the chicken over medium heat for 5 minutes before placing in oven.
6 Preheat oven to 225 ° C (fan: not recommended, gas mark 3-4 or about 425 ° F.) Place on the middle rack and roast for 15 minutes. Remove brick and turn the chicken. Roast for another 20 minutes until cooked through, reducing the heat slightly.
7 Remove the chicken from the oven, tent with aluminum foil and let rest for 5 minutes.