Salt the fish, sprinkle it with black pepper, pour lemon juice directly into the oven dish in which you will be roasting. Leave it for 20-30 minutes in the refrigerator.
Meanwhile, cook the cleaned and sliced mushrooms in 1 tablespoon oil. Salt them. Once soft, add the white wine, stir and gradually add the cream spoon by spoon.
Add some pepper and salt, if needed. Once the sauce bubbles, add some chopped fresh dill. Pour this sauce over the fish, top with small cubes of butter and put to bake for 30 minutes in a moderate oven. Optionally, cover with foil.