This is an incredibly satisfying and comforting dish the sweetness of the potatoes and celeriac, and the umami of the mushrooms and Parmesan see to that. It’s particularly good in tandem with simply cooked seasonal greens, but also with sides where there’s a sharpness that cuts through the dreamy slices of roots and their flavourful cooking stock.
Slow-roast lamb, confit duck legs or a sturdy white fish like monkfish or turbot are very well suited to this bake, which means your oven and you will be busy. No problem: it can be assembled in advance of cooking (add an extra 10 minutes, as the stock will be cold) and also reheats pretty well.
- Yield: 4 to 6 Servings
- 25 g dried porcini mushrooms
- 600–700 g sweet potatoes
- 600–700 g celeriac
- 70 g Parmesan, grated
- Leaves from 10 sprigs thyme
- 2 tablespoons cold-pressed rapeseed oil
- Sea salt and freshly ground black pepper
- Put the dried mushrooms in a heatproof mug or small bowl and pour 350 ml boiling water over them. Cover with clingfilm and leave to rehydrate and steep for 30 minutes, then drain and reserve both the mushrooms and the still-warm soaking liquid. Meanwhile, peel the sweet potatoes and celeriac and cut into 2–3 mm thick slices. This is easier and quicker on a mandolin. Preheat the oven to 200˚C/Fan 180˚C/Gas 6.
- The plan from here is to make alternating layers of the celeriac and sweet potato in a 1.5-litre ovenproof dish, with the porcini, Parmesan, thyme, salt and pepper as a seasoning. Aim for 3 layers of each root and 2 of porcini. Begin with the smallest, least regular bits of celeriac. Season with salt, pepper, a sprinkle of thyme and Parmesan, then add the sweet potato. Top that with porcini, salt, pepper, thyme and Parmesan, then repeat, making sure you use all the porcini the second time round. Add a third and final layer of celeriac, season, and then a third and final layer of sweet potato (arranging this one neatly, as it’s the top). Carefully pour the mushroom-soaking liquid into the dish – it might not seem like much, but celeriac is full of water and there’ll be plenty of cooking juices later on.
- Drizzle the oil over the top and finish with more salt, pepper, the remaining thyme and Parmesan. Bake for about 60 minutes, or until the top is nicely browned and the middle clearly warm, soft and cooked through. Press the top layer down from time to time with a fish slice or spatula – you’ll find that the cooking juices will rise and keep the top glistening and in good shape, rather than dry and curled. Allow to rest for 5–10 minutes before serving.