Preheat the oven to 180°C/350°F/Gas Mark 4.
Melt the butter in another large saucepan, add the leeks and cook for about 5 minutes until soft. Add the flour, stir well and then add the wine cook for 5 mins.
Add the milk and cream, basil pesto, lemon zest and juice. Keep stirring until all the liquid is incorporated and the sauce is smooth with no lumps. Season with salt and pepper.
Remove from the heat, add in the parsley, cubed fish and prawns. Stir everything to combine well.
Grease one large baking dish measuring about 25cm x 25cm. Transfer the mixture to the prepared dish. Mix the cheese with the breadcrumbs and sprinkle over the top of the gratin.
Place in pre heated oven for 25-30 minutes until golden-brown and the contents is bubbling.
Serving Suggestions
Serve the pie with some buttered peas and salad.
