Put the milk, fish and bay leaf in a large frying pan and gently poach for a few minutes until the fish flakes apart. Scoop out the fish and place to one side.
Melt the butter in a non-stick pan and stir in the flour. Cook for a moment, than add a little of the milk, stirring furiously with a silicone or wooden spoon or a whisk. The milk and butter/flour mixture will emulsify into a paste. Add a little more milk and repeat. Do this a couple more times until the mixture starts to look more like a sauce than a mixture. Add the remaining milk and heat gently until it thickens up. Simmer, very gently, for a couple of minutes until the floury taste is cooked out. Set to one side. Season with salt and pepper.
Boil the eggs for 5 minutes, adding the peas for the last minute, then drain and fill the pan with cold water to cool them off. Peel the eggs.
Peel, boil and mash the potatoes. Add the extra butter and mix well, season with salt and pepper.
Now assemble your pie. Very gently mix the flaked fish, peas and sauce together. Don’t mix too enthusiastically or the fish will disintegrate. Place in an oven proof dish. Slice the eggs into quarters and put on top of the fish and top with the mashed potato.
Your fish pie can now be safely stashed in the fridge for a day, maybe two. When you are ready to eat, heat in a hot oven until the mash is golden and the pie is hot all the way through. Enjoy with some veg on the side.