Instructions: Preheat the oven to 200C/400F/Gas 6.

1 Place the milk in a saute pan with the bay leaf, peppercorns and onion. Bring to a simmer and cook gently for a couple of minutes.

2 Set aside for at least 10 minutes to allow the flavours to infuse.

Add the fish to the infused milk and poach for 5 minutes or until just tender. Remove from the heat and leave to cool, then lift out the fish and roughly flake the flesh, discarding any skin and bone.

3 Place in a large bowl with the prawns and herbs. Strain the poaching milk into a jug. Melt half the butter in a pan and fry the shallots for 5 minutes to soften.

4 Add the mushrooms and cook for a few minutes until tender, then stir in the flour and cook for a minute or so, stirring constantly.

Remove from the heat and gradually add the poaching milk. Season, return to the heat and simmer for a few minutes. Keep stirring until thickened.

5 Stir in half of the cream and add a good squeeze of lemon, then fold into the fish mixture and season. Pour into a buttered 25cm/10in pie dish and set aside to allow a skin to form.

6 Place the potatoes in a pan of boiling salted water, cover and cook for 15-20 minutes until very tender. Drain, return to the pan to dry out and then mash until smooth.

7 Beat in the remaining butter and cream and the mustard. Season to taste. Carefully spread over the fish mixture and pull a fork across the top to make a wavy-line pattern. Bake for 30-40 minutes until bubbling and lightly golden. Serve hot.

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