2 red apples, such as Braeburn or gala, halved, core removed and sliced
2 tbsp cider vinegar
2 tbsp walnuts, plus extra for sprinkling
300g/10½oz cavolo nero, leaves torn in half
2 tbsp walnut oil
salt and freshly ground black pepper
Preheat the oven to 200C/180C Fan/Gas 6 and line a large baking tray with kitchen foil with a sheet of baking paper on top.
Rub a tablespoon of the butter over the plaice and season with salt. Lay two thirds of the thyme on the prepared baking tray and place the fish on top. Scatter over the rest of the thyme and the capers. Cover with another sheet of baking paper, folding the edges of the kitchen foil base to seal the parcel. Bake in the oven for 25 minutes.
Meanwhile, heat the remaining butter in a large frying pan and fry the celeriac with the garlic and some salt and pepper over a low–medium heat for 5 minutes. Add the apples to the pan and turn the heat up so that the apples and celeriac start to brown. Add the cider vinegar and walnuts and turn the heat down to low. Add the cavolo nero and cook for 5 minutes or until tender. Season with salt and pepper.
To serve, transfer the celeriac, apple and cavolo nero to a serving dish and scatter over a few extra walnuts and a drizzle of walnut oil.
Allow the plaice to rest in its parcel for 10 minutes before serving. Place the fish on a large platter in its parcel and take to the table for the grand reveal.