1. Preheat the oven to 375F, Gas Mark 5, 190C.
2. Put the fish in an ovenproof dish and pour over the milk
3. Sprinkle with salt and pepper and bake for 15 minutes before flaking fish
4. Strain the milk from the fish and reserve some for the sauce
5. Put the flaked fish back into bowl
6. In a medium saucepan, melt butter, add flour and mix well
7. Let the mixture bubble gently for 2 minutes, stirring continuously
8. Remove from heat and add milk stock, parsley and salt and pepper to taste
9. Bring back to the boil, stirring continually until sauce thickens
10. Pour over the fish
11. Boil the potatoes in salted water for about 20 minutes
12. Drain potatoes and mash with a little milk or cream, butter and pepper
13. Cover the fish with mashed potato and smooth over with a fork.
14. Sprinkle the cheese over the top and bake for 20-25 minutes until top is golden
15. Serve with fresh garden peas