Peel the potatoes and cut into even sized chunks. Place in a pan with sufficient water, cover and cook for 15-20 minutes or until soft.
Whilst the potatoes are cooking, lay the fish in a large frying pan and pour over sufficient milk to cover. Place the bay leaves and the peppercorns in the milk, cover and bring to the boil. Simmer gently for 8-10 minutes until the fish flakes apart. D
For the sauce, melt 75g butter in a pan over a low heat. Add the flour and whisk together. Cook for 2 minutes, stirring constantly then carefully whisk in the reserved liquid and further milk to make a creamy sauce. Season and add the ground nutmeg.
Prepare the fish by removing any skin and bones. Place in a large pie dish and gently break up the fish. Pour over the sauce and allow to cool for 5-10 minutes.
Pre-heat oven to 200°C/400°F/Gas Mark 6. Drain the potatoes and mash with 50g of butter and a little milk. Add the dried herbs and mix well. Spoon the mash over the fish and sauce and spread carefully. Bake in the oven for 25-30 minutes.
For the pea puree, place the peas in a pan with 100ml water. Bring to the boil and simmer for 5-6 minutes. Drain then add the seasoning and cream. Mix well. Crush with a potato masher and cook for a further 3-4 minutes.