Method
1. Heat the oil in a large pan over a medium heat. Add the onion and carrot and cook, stirring, for 5 minutes. Add the mince, turn up the heat and cook for 5 minutes, stirring until browned. Add the tomato purée, cook for 1 minute, then pour in the stock, Worcestershire sauce and thyme. Bring to the boil, then cover and reduce to a simmer for 20 minutes. Uncover and cook for 5-10 minutes, until most of the liquid is absorbed. Season, then spoon into a 2-2.5-litre ovenproof dish.
2. For the mash, cut the potatoes and parsnips into medium-size chunks and put into a large pan of cold salted water. Bring to the boil and simmer for 15 minutes, or until tender. Drain and return to the pan to heat for 30 seconds to drive off the excess moisture. Mash with the milk and nutmeg. Season and set aside. Preheat the oven to 180°C/fan160°C/gas 4.
3. Spoon the mash onto the mince. Rough up with a fork and sprinkle with the cheese. Bake for 25 minutes, until the mash is golden and crisp in places.