Slash each chicken piece 2 or 3 times with a small knife then put into a large plastic bag with the balsamic vinegar, wine, sage and some seasoning. Seal the bag well and chill for 3–4 hours or until required.
Cook the potatoes in a saucepan of boiling water for 4–5 minutes until almost tender, then drain well and tip into a large roasting tin. Add the parsnips, carrots and onion wedges, cover and set aside until required.
When ready to serve, tip the chicken and the marinade into the roasting tin. Drizzle the oil over the vegetables and sprinkle with a little seasoning. Roast in a preheated oven, 200°C (400°F), Gas Mark 6, for 40–45 minutes, turning the vegetables once or twice until golden and the juices run clear when the chicken is pierced with a small knife. Serve with a mixed leaf salad.