Preheat the oven to 220C/Gas7; grease a shallow ovenproof dish; heat the oil and butter in a frying pan until melted; add the leek, mushrooms and bacon, cover; cook over a low heat for 10 minutes, stirring occasionally, until tender
Lay the plaice fillets, skinned side up, on a board; divide the leek mixture between the fillets; fold over to cover the filling and place in the dish
Season the double cream with grated nutmeg, salt and freshly ground black pepper; pour over the fish fillets; sprinkle with grated cheese; bake for 20 minutes until the fish is tender and the cheese is melted and golden; garnish with parsley before serving
4 servings