1. Finely chop the rosemary and pound with the garlic and salt.
2. Place the chicken in a roasting tin and rub the oil all over chicken. Then rub in the rosemary mixture and sprinkle with pepper. If time allows, cover and refrigerate for up to 24 hours.
3. Preheat the oven to 220C / 425F / gas mark 7.
4. Cook the chicken for 10 minutes, then turn the oven down to 190C / 375F / gas mark 5 and roast for 20 minutes per 500g plus 10-20 minutes extra.
5. Thirty minutes from end of cooking time, remove the chicken from the oven and drizzle with the balsamic vinegar. Return to the oven and allow the skin to crisp.
6. Serve garnished with rosemary sprigs alongside a selection of vegetables.