Season the plaice fillets and roll them up Swiss roll fashion. Secure each roll with a cocktail stick and poach gently in the milk for about 10 minutes in a preheated oven, 180°C (350°F)/Gas Mark 4.

Drain the fish and allow it to cool. Remove the cocktail sticks. Increase the oven temperature to 200°C (400°F) Gas Mark 6.

Put the mushrooms and butter into a pan with the lemon juice. Cook over a moderate heat for about 5 minutes.

Allow the mushrooms to cool and then stir in the stuffing mix.

Roll out the pastry, quite thinly, into 4 circles, each 6 inches in diameter. Brush the edges with beaten egg.

Put a fish roll into the centre of each pastry circle and top with a quarter of the mushroom mixture. Pull the pastry edges up and over the fish and pinch together to seal.

Place the turnovers on a greased baking sheet and glaze with the beaten egg. Sprinkle with a few poppy seeds.

Bake in the reset oven for about 25 minutes, or until well risen, puffed and golden. Serve piping hot.