Here’s a picture of the Russian Fish Pie I made a few weeks back. I would blog it but I’ve lost the recipe card it’s from. All I can say is it involved puff pastry, smoked haddock, fresh parsley and a simple roux and it was delicious.
(Yes, I did burn it a little. It was still GREAT.)
Puffed by Alix

Ye olde school book, ‘Cooking Explained’ by Barbara Hammond, has a similar version using filleted white fish, lemon juice and a hard-boiled egg in the filling. Yours looks tasty.
Now you mention it, this had hardboiled egg in it as well.