Serves 6 to 8 people.
Takes 15 minutes to prepare on the stove top, then bake in the oven at 200F, Gas 6, 400F to melt the topping.
1. Oil a deep ovenproof dish and turn on the oven to heat.
2. Put the haddock and monkfish (if available) into a deep lidded pan. Pour in the milk, add the bay leaf and lemon juice and rind and bring to the boil. Turn down the heat to simmer, cover the pan and cook the fish for 4 to 5 minutes.
3. Add the prawns and simmer for another 2 minutes, then turn off the heat.
4. Drain the fish into a clean dish, add the flaked salmon and reserve the cooking juices to make the sauce.
5. Make the sauce by heating the rapeseed oil in a saucepan on medium heat, stir in the flour and dried mustard to make a smooth roux. Stir in the pan juices off the heat. Return to the hob, stirring all the time till the sauce boils to thicken. I like to use a balloon whisk – it’s great for getting rid of lumps!
6. Taste the sauce, season with sea salt and ground black pepper and a squeeze of lemon juice to bring out the flavours. Gently stir in the parsley and fish, then pour into the prepared dish.
7. Quickly make the topping by tossing the oats, oatcakes, oil and a little ground black pepper, in a bowl, then mix in the cheese.
8. Scatter over the fish, and bake in the middle of the hot oven for 8 to 10 minutes until golden and bubbling.
Any mix of firm fish are suitable for this pie.
I used rapeseed oil and coconut milk to make a healthy base to compliment the topping. A richer version made with butter and milk works well too.
Try a spoon of chilli-infused rapeseed oil in the topping to add some spice.
You can heat the pie in the microwave on bursts of 1 minute and crisp the topping under a medium hot grill but watch as it burns easily.