Cut the fish into 2 cm pieces. Make sauce by melting butter in a saucepan, add flour, cook stirring for 2 minutes. Remove from heat, gradually stir in milk until smooth. Add cheese, wine and salt and pepper to taste. Cook, stirring, over gentle heat till sauce has thickened, lower heat and cook stirring for a couple of minutes. Set aside to cool.

Line a deep pie dish with 2 sheets puff pastry, pressing sheets together to seal join in base. Trim edges, prick base with a fork and bake in 350° oven for 10 minutes, then cool to room temperature.

In a large steamer, steam carrots, spring onions, tomatoes, celery, garlic, and bay leaves for 10 minutes. Add the fish, steam for 5 more minutes. Add the scallops and prawns and steam for 2 more minutes. Remove from the heat and take out the bay leaves. Spoon seafood and vegetable mixture into pastry case, sprinkle with parsley/basil. Pour the white sauce over and cover with 2 remaining sheets pastry. Seal and trim edges, prick pastry top and lightly baste with milk. Bake at 400° for 15 minutes or until top is golden brown.