1 Preheat the oven to 180°C (160° fan) | 350F | gas 4.
2 Remove a few inner pieces of onion from the onion halves and arrange them cut-side up in a roasting tray.
3 Toss together 50 ml of the oil with the cranberries, blackcurrants, Parmesan, leek, crushed red pepper, half the parsley, and plenty of seasoning.
4 Spoon into the red onion halves and drizzle them with the remaining oil. Roast for 40 - 45 minutes until tender.
5 Remove from the oven and leave to cool briefly before serving on a platter with a garnish of the remaining parsley.