Preheat your oven to 350° F. In the meantime, melt 1 tbsp of butter in a medium saucepan over medium heat. Add the mushrooms and cook until they are tender, stirring from time to time.
Use 1 tbsp of butter to grease the casserole (½ quart) and mix your seafood components on it, topping them off with the cooked mushrooms.
Prepare the sauce. Add the remaining 3 tbsp of butter to a saucepan over medium-low heat. Whisk in the flour until it’s smooth and bubbly. Cook for another 2 minutes stirring constantly.
Add the milk gradually, constantly stirring. Reduce the heat and continue stirring until the sauce is thickened and the mixture turns to a light sauce. Add salt, pepper, chives, paprika, parsley, and wine.
Pour the sauce into the seafood casserole, mix it, and bake for 8-10 minutes in a preheated oven.
Remove the dish from the oven and sprinkle the parmesan cheese on top of it. Pro tip: you can also use breadcrumbs for a crunchy top.
Return the dish to the oven and bake for another 8-10 minutes until it has a brown and pleasant top. Serve immediately and enjoy!