• 1 kg (2 lb 4 oz) potatoes, peeled and quartered
• 400 g (14 oz) parsnips, peeled and cut into chunks
• fine sea salt
• 150 ml (5 fl oz) non-dairy milk, warmed, plus a little more if needed for thinning
• 60 ml (2 fl oz/¼ cup) olive oil
• freshly ground black pepper
• 40 g (1½ oz) dried porcini mushrooms
• 600 ml (21 fl oz) hot water
• 750 ml (26 fl oz/3 cups) porcini mushroom stock (vegetable stock is fine)
• 270 g (9½ oz/1¼ cup) green or brown lentils, rinsed
• 2 bay leaves
• 1 onion, finely chopped
• 2 medium carrots, diced small
• 2 garlic cloves, minced
• 2 tablespoons chopped thyme
• 500 g (1 lb 2 oz) mushrooms, such as chestnut, portobello, oyster or wild, sliced
• 3 tablespoons tomato paste (concentrated purée)
• 100 g (3½ oz/⅔ cup) frozen peas
• 1 tablespoon cornflour (cornstarch)

Cook the potatoes and parsnips in simmering salted water for 20 minutes, or until tender. Drain, return to the pan and mash with the warm milk and 2 tablespoons of the olive oil. Season with salt and pepper and set aside.

Cover the porcini mushrooms in the hot water and set aside. Meanwhile, simmer the stock, lentils and bay leaves for 20 minutes, or until tender. Drain off any excess water and discard the bay leaves.

Meanwhile, heat the remaining olive oil in a pan and fry the onion, carrot, garlic and thyme until soft and caramelised, about 15 minutes. Heat the oven to 180°C (350°F/Gas 4).

When the onion has almost finished cooking, drain the porcini mushrooms, reserve the soaking liquor and chop. Add to the onion mixture, then stir in the fresh mushrooms, tomato paste, peas and flour and cook for 1 minute. Add the porcini soaking liquor and lentils. The lentils and mushrooms should be bathed in sauce, so add a little water to loosen. Season generously with salt and pepper.

Pour lentil mixture into a 30 x 25 cm (12 x 10 inch) ovenproof dish. Spoon over the mash (beat in a little more milk if too thick) and spread it right up the edges with the back of a spoon. Bake for 40 minutes, or until bubbling and golden on top. Leave to stand in the ovenproof dish for 5 minutes before serving.