This reminds me of the pie in Kiki’s Delivery Service!
It looks delicious, and maybe you could link the recipe.
Recipe (of sorts because I always wing it and refuse to measure anything unless on pain of death)
Peel and boil some potatoes until soft then mash adding a little butter and put aside to cool.
Fry off some leeks and garlic with seasoning until soft and put aside.
In a pan of just simmering milk add a fish stock cube and then gently poach your fish (ideal mix for me is salmon, coley which is chronically underrated and smoked haddock)
Remove the fish once nearly cooked and put aside
Make a basic rue using butter and flour and then add the milk used to poach the fish until a sauce is created.
Mix the leeks, fish, sauce with peas and spinach in an oven proof dish and set aside.
With the cooled mashed potatoes add an egg and flour and mix until a dough forms (you may need to add a little water) - you can also add parmesan/mustard/herbs to the dough if you wish.
Tip the dough onto a floured surface and kneed/roll/cut out as wished.
Add the pastry to the top of the fish pie. Egg wash and bake until golden.