Salmon and haddock sweet potato fish pie

Potato topping

• 800g sweet potatoes, peeled and cut into 2cm cubes
• 20g unsalted butter
• Good pinch of freshly grated nutmeg
• Pinch of sea salt and freshly ground black pepper

Fish filling

• 2 tbsp cornflour
• 300ml semi-skimmed milk
• 700g mix of haddock and salmon, skinless, cut into bite-sized chunks
• 150g frozen peas
• ½ bunch of spring onions, sliced
• Fronds from 1/3 bunch of fresh dill, finely chopped
• 100g low fat crème fraiche
• Freshly ground black pepper

1. Preheat the oven to 200C (fan 180C), 400F, Gas Mark 6.
2. Bring a medium pan of salted water to the boil and cook the potatoes for 10-12 minutes or until tender. If you steam the potatoes, they tend to take on less water, making for a crisper (and better) sweet potato mash.
3. As the potatoes cook, put the cornflour in a wide pan with a little of the milk and stir until dissolved and smooth. Then add the rest of the milk, stirring all the time.
4. Place on a low to medium heat, and continue to stir as you bring it to a simmer. Cook for a few minutes until it thickens. Then add the fish, peas, spring onion, dill and cook gently for about three minutes, stirring to stop it from catching on the pan bottom.
5. Stir in the crème fraiche and add salt and pepper to taste. Remove from the heat and tip in to a 2.5 litre ovenproof dish (minimum size: 25cm square; 6cm deep).
6. Once the potatoes are cooked, drain  and tip them back into the pan. Add the butter, nutmeg, salt and pepper (if needed) and mash until smooth,.
7. Spoon the mash over the fish filling, then spread it evenly with a fork. Grate over a little more nutmeg and pop it on a baking tray in the oven for about 20 minutes until the top is just catching colour and the fish filling is piping hot. Serve at once.