- Cook the fish. 
- Place the smoked haddock (skin side down) along with the other fish in a pan, and pour enough of the 20 oz (590 ml) of milk just to cover them. Remove the fish, bring the milk to a boil, then put the fish back in, reduce the heat, and simmer over low heat for 4 minutes. 
- Remove the fish from the milk and allow to cool, then remove the skin from the smoked haddock. Strain the milk into the jug with the milk from the original amount, and set aside.  
- Put the potatoes in a separate pot and cover with water with ¾ tsp Kosher salt. Bring to a boil, then simmer for about 13 minutes or until they are ready, then drain thoroughly. While the potatoes are cooking... 
- In another pot over medium high heat, add one tablespoon of butter and leeks, and sauté for a few minutes until the leeks are a bit transparent, but not brown. Remove the leeks and set aside. 
- Put the other tablespoon of butter into the pan, then add the flour. Cook for a few minutes without browning or the flour will taste raw. Begin adding a little of the measured milk into the pan a little at a time. Mix it well each time before adding more. 
- Continue adding the milk until it's finished.  
- When the sauce is ready, add about ½ tsp salt and some white pepper, then add the leeks. 
- Flake the cooled fish into pieces. 
- Next, add the fish to the sauce with the leeks and still well, but try not to break the pieces of fish any more. Taste for salt and pepper and adjust as needed. 
- Spoon into ramekins and allow to cool while mashing the potatoes which should be ready. 
- Preheat oven to 400℉ (200℃.) 
- Mash the potatoes while still hot, adding salt, butter, and milk. If not soft and creamy, add more butter or milk, and salt if needed. Add a beaten egg after the potatoes have cooled a little and mix well. 
- Either pipe the potatoes onto the fish pot pie in the ramekins or baking dish. I used a 1M tip, or, spoon the mashed potatoes on evenly and spread with a fork. I do prefer piping, but the flavor is the same. 
- Use the fork to decorate the top. Place on a baking tray for easier handling. 
- Bake the fish pot pie in preheated oven for about 30 minutes or until the potato topping is golden brown and the sauce is bubbling. 
- Serve and enjoy while hot! Be sure to warn diners that the ramekins are very hot, too. 
- Children love these, too, so don't hesitate to make smaller ramekins for them.