Heat 1 tbsp oil in a large saucepan and fry the mince until browned – you may need to do this in batches. Set aside as it browns. Put the rest of the oil into the pan, add the vegetables and cook on a gentle heat until soft, about 20 mins. Add the garlic oil and tomato purée, increase the heat and cook for a few mins, then return the beef to the pan. Pour over the wine, if using, and boil to reduce it slightly before adding the stock, Worcestershire sauce and herbs. Bring to a simmer and cook, uncovered, for 45 mins. Check after about 30 mins – if a lot of liquid remains, increase the heat slightly to reduce the gravy a little. Season well, then discard the bay leaves and thyme stalks.
Mix the cornflour with some water (2 tbsp) in a glass until it is all dissolved but not too runny. Add this to the mixture and heat until thickened.
Meanwhile, make the mash. In a large saucepan, cover the potatoes in salted cold water, bring to the boil and simmer until tender. Drain well, then allow to steam-dry for a few mins. Mash well with the rice milk, olive oil, and three-quarters of the parmesan cheese, then season with the nutmeg and some salt and pepper.
Spoon meat into 2 ovenproof dishes. Pipe or spoon on the mash to cover. Sprinkle on the remaining cheese. If eating straight away, heat oven to 220C/200C fan/gas 7 and cook for 25-30 mins, or until the topping is golden. Or follow the steps (below) to freeze.