Preparation

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  1.
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  Preheat the oven to 190 degrees, 170 degrees fan oven. Lightly grease an ovenproof dish with butter.
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  2. First prepare the vegetables. Peel the onion, cut it in half and slice it finely. Trim and wash the leek and slice it fairly thinly. Peel the sweet potato, the swede and the carrots, cut them into 4 pieces lengthways then slice them very thinly. Wipe the mushrooms and slice them quite thickly.
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  3. Heat the sunflower oil in a large saucepan and sauté the onion over a low heat for 3-4 minutes. Add the leek and the garlic, peeled and crushed, and cook for a further 2-3 minutes. Stir in the mushrooms and season with plenty of salt and pepper.
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  4. Stir the mustard into the hot vegetable stock then pour it into the pan. Mix the milk and the cream together and add them too. Bring to a simmer and cook to soften the vegetables, for about 12-15 minutes. Then add the thyme leaves and adjust the seasoning if necessary.
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  5. While the vegetables are cooking, make the topping. Chop the walnuts finely, cut the crusts off the bread and turn it into breadcrumbs. Mix the two together in a bowl then stir in the grated cheese.
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  6. Spoon the vegetable mixture into the prepared dish and sprinkle the topping on evenly. Bake for 30-35 minutes, until the topping is crunchy and golden brown.