Vegan Lentil and Mushroom Parmentier

Place the dried porcini in a small bowl, pour over the boiling water, and set aside to rehydrate for 20 minutes. Once softened, lift the porcini out, squeeze excess liquid back into the bowl, and finely chop the mushrooms. Strain the soaking liquid through a fine sieve lined with kitchen paper and reserve. Rinse the lentils, dice the onion, mince the garlic, dice the carrots and celery, and chop both varieties of fresh mushrooms.

Place the lentils, vegetable stock, bay leaf, and thyme sprig in a medium saucepan over medium-high heat. Bring to a boil, then reduce to a gentle simmer and cook for 20-22 minutes until the lentils are just tender but holding their shape. Drain, discard the bay leaf and thyme sprig, and set aside.

Heat a large cast-iron or heavy-based frying pan over high heat until smoking. Add 1 tbsp olive oil and spread the chestnut and portobello mushrooms in a single layer — do not stir. Cook for 5 minutes until deeply browned on one side, then season generously with salt and pepper, toss, and cook for a further 3 minutes. Transfer to a bowl and set aside.

Return the pan to medium heat, add the remaining 2 tbsp olive oil, and cook the onion and celery for 6-7 minutes, stirring occasionally, until soft and lightly golden.

Add the garlic and carrots to the pan and cook for 3 minutes, stirring, until the garlic is fragrant.

Stir in the tomato purée and cook for 2 minutes, pressing it against the base of the pan until it darkens slightly.

Pour in the red wine and cook for 3 minutes, scraping up any browned bits, until the wine has reduced by half.

Add the chopped porcini, the reserved porcini soaking liquid, the soy sauce, and fresh thyme leaves to the pan. Stir to combine and simmer for 5 minutes until the liquid has reduced to a glossy, coating sauce.

Fold in the cooked lentils and browned fresh mushrooms. Taste and adjust seasoning. Transfer the filling to a deep 25 × 20 cm baking dish, spreading it into an even layer.

Meanwhile, place the potato chunks in a large saucepan of cold salted water. Bring to a boil over high heat, then reduce to a rolling boil and cook for 18-20 minutes until completely tender when pierced with a knife.

Drain the potatoes thoroughly and return them to the dry pan over low heat for 1 minute, shaking gently, to steam off excess moisture. Remove the pan from the heat. Pass the potatoes through a ricer or mash until completely smooth. Beat in the warm oat milk, extra-virgin olive oil, Dijon mustard, and nutmeg. Season generously with salt and white pepper.

Preheat your oven grill (broiler) to high. Spoon the mashed potato over the lentil filling and use a fork to rough up the surface into peaks and ridges — these will catch and crisp under the grill.

Bake in the centre of the oven at 190°C, or 375°F, or gas mark 5 for 20 minutes until the filling is bubbling at the edges.

Transfer the dish under the preheated grill for 5-7 minutes, watching closely, until the potato peaks are golden and crisp. Scatter over the chopped parsley and serve immediately from the dish.