- Place the coley (saithe) and salmon in a saucepan with the milk, bay leaves and onion slices. Season with salt and pepper and bring to a gentle simmer, cook for 2 to 3 minutes and then place a lid on the saucepan, take it off the heat and allow to infuse for 30 minutes.
- After 30 minutes, remove the fish from the milk with a slotted spoon and place the fish into a bowl, adding the prawns and mixing gently, as not to break the fish up.
- Remove the bay leaves and onion slices from the milk and pour the milk into a jug.
Mashed potato topping:
- Boil the potatoes for 20 to 30 minutes until very soft. Drain the potatoes and then add the butter and mash with a potato masher until smooth and fluffy. Season to taste and add three quarters of the grated cheese and mix well.
- Pre-heat oven to 200C/400F/Gas 6.
- Melt the butter in a saucepan and stir in the flour, keep stirring until the mixture resembles sand, then start to add the infused milk gradually, whisking all the time until the all the milk is used up and you have a thick, smooth sauce. Check seasoning and adjust.
- Add the chopped chives and parsley, and stir well.
- Spoon a little of the white sauce on the base of a deep enamel pie dish or another suitable oven-proof dish.
- Arrange the fish and prawns over the top of the sauce and then add the rest of the sauce.
- Smooth the top of the sauce and then carefully add the cheesy mashed potatoes, ensuring that the potatoes go right up to the edges of the pie dish.
- Take a teaspoon and press the back of the bowl into the mashed potatoes to give the effect of fish scales and then sprinkle the rest of the grate cheese over the top.
- Place the pie into the pre-heated oven and cook for 25 to 30 minutes or until the top is golden brown and the filing is bubbling.
- Serve hot with fresh garden peas, or other seasonal vegetables such as courgettes, carrots and green beans.