Heat the olive oil in a large saucepan and fry the onion, carrots and mushrooms for 10 minutes until softened.
Add the minced beef, season with salt and pepper and stir frequently with a wooden spoon for 5 minutes, separating any clumps of meat.
Add in the wine and simmer for about 10 minutes, stirring occasionally until the alcohol has evaporated.
Add the tomatoes and basil, taste for seasoning and cook, uncovered, over a medium heat for 30 minutes.
Meanwhile, preheat the oven to 200°C/400°F/gas mark 6.
Cook the sweet potatoes in boiling salted water until soft. Drain and mash well, adding in the butter, milk and 100g of the Parmesan. Season with salt and pepper, then stir vigorously with a wooden spoon over a low heat for 2 minutes to give a creamy texture.
Pour the meat sauce into your pie dish(es) and carefully spread over the mashed potato, ensuring that the meat is completely covered.
Use a fork to create small peaks and then sprinkle the remaining Parmesan on top.
Bake in the centre of the oven for about 20 minutes or until the topping is crisp and golden. Serve immediately.