Preheat the oven to 200°C, fan 180°C, gas 6. Put the olive oil in a roasting tin and put in the oven to heat for 5 minutes.
Add the parsnips, potatoes, carrots and onion to the tin along with the rosemary and garlic. Roast for 30 minutes.
Crumble over the chestnuts, then drizzle over the maple syrup. Mix well, then roast for a further 15-20 minutes, until golden.
Cook’s tip: if your vegetables look like they are beginning to dry out during roasting, drizzle some apple juice or vinaigrette over the top.