Heat 1 tablespoon of the oil in a frying pan, add the mushrooms and cook for 5 minutes until softened.
Stir in the hazelnuts, then remove from the heat and stir in the parsley.
Lay the plaice fillets on a clean surface and divide the mushroom mixture between them, then roll up to enclose the stuffing.
Place each fillet on a piece of foil large enough to enclose it, sprinkle with the white wine, season with pepper, add 1 piece of the butter and seal well.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 15 minutes, or until cooked through.
Meanwhile, cook the potatoes in a saucepan of boiling water for 12–15 minutes until tender.
Heat the remaining oil in a frying pan, add the lettuce and fry for 2–3 minutes on each side.
Drain the potatoes and season, then add the mint and lightly crush with a fork.
Top with the plaice parcels and serve with the lettuce.
Notes / Tips / Wine Advice:
For plaice & mushrooms with hazelnut broccoli,
put 4 plaice fillets in an ovenproof dish and cover with 225 g sliced mushrooms. Sprinkle with the juice of 1 lemon and season. Dot with 25 g butter and bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 16–17 minutes, basting frequently. Pour over 150 ml single cream and brown under a preheated hot grill. Meanwhile, cook 350 g Tenderstem broccoli in a steamer for 3–4 minutes until tender. Toss together with 2 tablespoons olive oil and 3 tablespoons chopped hazelnuts. Serve with the plaice.