Golden Fish Pie

Ingredients

1kg potatoes

1 lemon

40g unsalted butter

400g frozen peas

2 carrots

2 onions

olive oil

500ml semi-skimmed milk

2 x 150g frozen salmon fillets

2 x 100g frozen white fish fillets

65g plain flour

100g frozen spinach

125g frozen cooked 
peeled prawns

1 heaped teaspoon 
English mustard

40g cheddar cheese

Instructions
Preheat the oven to 180ºC/350ºF. Peel the potatoes and cut into large chunks, then put them into a large pan of boiling salted water for 15 minutes, or until cooked through. Drain and mash with a pinch of salt and pepper, the zest from the lemon and the butter. Place the frozen peas in a colander, pour over some boiling water to defrost them, then drain well and pulse a few times in a food processor. Fold them through the mashed potato, then leave to one side.

Peel and chop the carrots and onions and cook them in a large ovenproof pan (roughly 30cm in diameter) with a lug of oil for 15 minutes, or until softened but not colored, stirring occasionally. Meanwhile, heat the milk in a pan on a medium heat. Once simmering, add the frozen fish fillets for around 10 minutes, or until cooked through, then use a slotted spoon to remove them to a plate, taking the pan off the heat.

Stir the flour into the carrots and onions, then gradually add the milk, a ladleful at a time, stirring continuously. Stir in the spinach until broken down, then season to perfection. Flake in the fish fillets (carefully remove and discard the skin if the fillets have it), add the prawns, mustard and the juice from half the lemon, grate in the Cheddar and stir gently to combine. Top with the pea-spiked mash and smooth out, scuffing it up slightly with a fork to give it great texture. Bake for 30 to 40 minutes, or until beautifully golden.