1/2 stick butter
1 c. fish stock (cook fish meat with seasonings and water)
1 (8 oz.) can mushrooms
1/2 c. skim evaporated milk
1/2 c. heavy cream
2 tbsp. flour
Garlic salt to taste
Salt and pepper to taste

Melt butter in a small saucepan. Saute mushrooms and onions. Mix rest of ingredients stirring constantly. Let the sauce come to boil then remove from heat. You can add chopped parsley, capers if desired; before serving on top of fish, which has to be baked already. Serve hot.