A delicious fish dish, we knew about that combination from childhood - it was a relative of ours with freshly caught carp from the river. I haven't tried it yet and I'm sorry, it's really tasty and special. I think you can use the fish you prefer - I made it with carp, I would recommend salmon, trout, sea bream, etc.
I bought the sour cream from the market and it was like cheese - it didn't confuse the taste, but next time I would make it with heavy cream (or country cream), to make the sauce more homogeneous.
The fish is cleaned well, cut into pieces.
Mix sour cream with green onions and chopped parsley, season with salt and pepper.
Add this mixture to the fish, mix well with your hands.
Sprinkle a deep baking tray with a little oil.
Cut the white onion into rounds and arrange a layer on the bottom of the tray.
Put the fish pieces on the onion, pour the sauce on top with the greens.
Put in the oven for 1 hour at 180-200 degrees, notice that it will make a nice crust on top.
Serve hot with any vegetable garnish or polenta.
Good appetite!