400 g frozen peas (ideally petit pois)
400 g undyed smoked haddock fillets (skinned)
400 g fish (e.g. salmon, gurnard, hake) (skinned)
500 ml whole milk
1 bay leaf
1 kg King Edward potatoes
50 g butter
100 ml whole milk
Sea salt and ground white pepper (black pepper is also fine to use)
Béchamel, cheese & herb sauce
40 g butter
40 g plain flour
40 g cheddar cheese, grated
1 tsp Worcestershire sauce
1 tsp English mustard powder
Pinch of freshly grated nutmeg
25 g tarragon, leaves picked and roughly chopped
25 g dill, leaves picked and roughly chopped
2 spring onions, thinly sliced
30 g grated cheddar
30 g fresh breadcrumbs
12-18 clams (even in size and washed well in cold water; discard any that are not tightly closed)
Preheat the oven to 220°C / 200°C fan / gas 7.
Blanch the peas for 1 minute in boiling salted water, then drain and rinse under cold running water (cooling quickly helps retain the vibrant colour). When cold, roughly blitz the peas in a blender and spread evenly over the base of the baking dish.
Cut the fish into large chunks and remove any pin bones. Place the fish in a saucepan with 500 ml milk and the bay leaf. Cover with a lid and bring gently to the boil, then remove from the heat and allow to cool. Remove the fish from the milk (keeping the milk for the béchamel sauce), break into large chunks and set aside in a bowl.
Peel the potatoes and cut into 3 cm chunks, cook in boiling salted water for 12 minutes, or until tender. Strain and leave to steam in the sieve for 10 minutes. Warm 100 ml milk and 50 g butter in a saucepan, add the cooked potato and mash until smooth (use a ricer for a super smooth texture). Season well and set aside.
Melt 40 g butter in a saucepan, then stir in 40 g flour and cook for 1 minute over a moderate heat, stirring constantly. Gradually add the milk used to poach the fish, stirring well to avoid lumps forming. Simmer for 5 minutes until the mixture thickens and becomes glossy. Remove from the heat, stir in the grated cheese, Worcestershire sauce, mustard and nutmeg, and season to taste. Pour the sauce over the fish pieces, and gently stir in the chopped herbs and spring onions. Spoon the mixture over the top of the peas in the baking dish.
Top the fish with the mashed potato, starting at the edge of the dish and working inwards. Use a fork to fluff the top, sprinkle over 30 g grated cheddar and 30 g of breadcrumbs. Bake in the oven for 20 minutes, then remove and place the clams on top, gently pressing them halfway into the potato. Return to the oven and cook for another 10 minutes, until the clam shells have opened up, and the top of the potato is crispy and golden.