A classic comfort dish topped with sweet potato mash
Preheat the oven to 180°C/fan 160°C/gas mark 4.
Boil the sweet potatoes until tender, around 10-15 minutes. Drain and allow to steam dry.
While the potatoes are cooking, prepare the filling. Put the haddock in a pan large enough to fit the fillets in a single layer. Tuck in the bay leaves and scatter over the onion. Pour over the milk and season with salt and pepper. Bring to a steady simmer, cover with a lid or tight-fitting piece of foil and poach until the haddock is cooked all the way through, around 10 minutes.
Using a slotted spoon, remove the cooked fish to a plate and allow to cool a little. When cool enough to handle, flake with a fork.
Put the flaked haddock in an oven-proof baking dish and evenly scatter over the prawns.
In a clean saucepan, melt 50g of the butter, then stir through the flour. Cook over a gentle heat for a couple of minutes. Gradually add the poaching milk, including the onions (remove the bay leaves though). Whisk constantly over a medium heat for about 5 minutes until the sauce is thick and smooth. Season, stir through the parsley and dill and pour the sauce over the fish, spreading it evenly.
Add the remaining butter to the drained sweet potatoes and mash until smooth. Season with salt and pepper to taste.
Spread the potato over the fish and sauce filling and fluff up the top with a fork. Bake in the oven for 30 minutes until the pie is bubbling and the top golden and crisp. Serve with green vegetables.