Cheesy fish pie with mustard mash

This recipe makes three pies, which each serve 3-4 people. Make them at the weekend, then defrost during the week and pop in the oven to have dinner on the table in just over half an hour.

Ingredients

9-12 (3 pies, each serving 3-4)

Ready in: 35 mins, plus cooking from chilled or frozen

Suitable for freezing

• 800g-1kg fish fillets (we used a mixture of cod, salmon and smoked haddock)
• 950ml semi-skimmed milk
• 1 onion, halved
• 1 bay leaf
• 1.5kg white potatoes, peeled and chopped into small chunks
• 80g butter
• 150g Cheddar, grated
• 2 tsp English mustard
• 50g plain flour

Method

1. Put the fish fillets skin-side up (if using fish with skin) in a large, deep pan. Pour over 800ml of the milk, and add the onion and bay leaf, plus some black pepper. Bring to a gentle simmer, then turn off the heat and leave to infuse for 10-15 mins.
   
2. Meanwhile, cook the potatoes in boiling water for 10-12 mins, or until a cutlery knife goes through easily. Drain and allow to steam dry in a colander. Tip back into the pan and mash with 30g of the butter, the rest of the milk, three-quarters of the Cheddar and the mustard. Season with salt and pepper.
   
3.  To make the sauce, strain the milk from the fish into a jug. Add the remaining butter to a small saucepan over a medium heat. Once melted, add the flour, stirring continuously until a paste forms. Continue cooking for 1 min, stirring all the time.
4.  Add the infused milk to the flour mixture, a little at a time, using a whisk to beat into a smooth sauce. Bring to a simmer, stirring all the time – you will feel the sauce start to thicken. Once bubbling, cook for 2-3 mins, stirring often, until you have a thick, smooth, lump-free sauce. Season with salt and pepper.
5.  Peel the skin from the fish and break up roughly, dividing the pieces between 3 enamel or glass pie dishes (each serving 3-4). Pour over the sauce, then top with the mustard mash and sprinkle over the remaining cheese. Once cool, wrap in cling film and freeze until required.
6.  To cook from frozen, pre-heat the oven to 160°C/fan 140°C/gas 3. Unwrap the clingfilm from the pie and cover with foil. Bake in the oven for 1 hr 15 mins-1 hour 30 mins, or until you can easily push a knife through the middle of the pie. Remove foil, turn heat up to 220°C/fan 200°C/gas 7, and cook for 30-35 mins more, until the top is golden and the filling is piping hot. Alternatively, defrost the pie overnight in the fridge and cook for 30-35 mins at 200°C/180°C fan/gas 6.