Pea & celeriac crusted fish pie

Put the potatoes and celeriac in a large saucepan of salted water. Partially cover with a lid, bring to the boil and cook for 15 minutes. Carefully put the eggs on top, cover and boil for a further 5 minutes. Use a slotted spoon to transfer the eggs to a bowl of iced water and cool completely. Add the peas to the pan, cover and bring to the boil. Drain, steam dry for 5 minutes, then mash with 30ml milk. Season and set aside.

Meanwhile, put the bay leaves, fish pie mix and prawns in a large frying pan. Pour over the remaining 300ml milk, partially cover with a lid and bring to a simmer; cook for 2-3 minutes. Remove from the heat, leave to cool slightly, then transfer the fish to a plate. Strain the milk into a measuring jug. You want 300ml of liquid, so top up with more milk if needed. Preheat the oven to 180°C, gas mark 4.

For the sauce, melt the butter in a pan until foaming. Add the flour and stir to make a thick paste. Cook, stirring, for 2-3 minutes until golden. Remove the pan from the heat, then gradually add the poaching milk, beating until combined between each addition. Simmer over a medium heat for 5-7 minutes, stirring constantly, until thickened. Mix in the lemon zest and juice and crème fraîche; season.

Peel the eggs, quarter and scatter into a medium-large baking dish with the fish and prawns. Pour over the sauce and top with spoonfuls of the mash, spreading evenly to cover. Press gently all over with the back of the spoon to create a scalloped effect. Put on a baking tray and bake for 30-40 minutes, until bubbling with a lightly browned, verdant green crust, the prawns are opaque and the fish flakes easily.