How to cook
Cut the fish, peel the shrimp and clean the mussels.
Saute the onions in half the butter, then add the mussels and 3-4 tbsp water. Put a lid on and saute until the shells open up.
Drain out the broth and pour it into a pot with the wine. Put in the fish and saute 5-8 min. Take the fish out and boil the broth.
Mix the flour with the remaining butter and add this to the liquid, stir until thickened.