Preheat oven to 220°C.
Rub chicken inside and out with lemon.
Crush garlic, roll in salt and pepper, and insert in cavity with lemon halves, rosemary sprig, and butter.
Put chicken into a large baking dish.
Season vegetables with salt and pepper, add rosemary leaves and oil, and toss to coat.
Scatter vegetables around chicken and massage its skin with seasoned olive oil.
Turn chicken on its side.
Place baking dish in centre of oven.
After 20 minutes, turn chicken over onto its other side and carefully turn vegetables.
After a further 20 minutes, turn chicken breast-side up, baste with juices, loosen vegetables, and roast for another 20 minutes.
Reduce oven temperature to 160°C.
Transfer chicken and vegetables to a heatproof plate and rest in oven.
Discard all fat from baking dish and deglaze over heat with wine.
Stir vigorously to dislodge cooked-on bits, and lengthen with more wine or stock.
Joint chicken, arrange on a serving platter with vegetables, and pour over juices.
