Preheat the oven to Gas Mark 5, 190ºC, fan 170ºC. Put the potatoes in a large pan and cover with water. Bring to the boil and cook for 10-15 minutes until cooked through. Drain and mash, adding a little milk if you wish. Season with salt and pepper.
Meanwhile, heat the oil in a large saucepan and gently cook the onion for 5-10 minutes, until softened. Add the soft cheese and the stock and combine well.
Blend the cornflour with 2 teaspoons of cold water and stir into the sauce. Cook for a few more minutes until thickened. Add the fish pie mix and cook for 2 minutes before stirring in the prawns and parsley.
Pour into an oven dish and top with the mash. Cook for 25-30 minutes until piping hot.
Freezing and defrosting instructions
This recipe can be frozen for up to 3 months before cooking in the oven. To reheat, defrost at room temperature for 1 hour and bake for 30 minutes at 180C/350F/Gas Mark 4.