Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   2      tablespoons   vegetable oil
   2      tablespoons   flour -- all-purpose
   1 1/2  cups          fish stock
                        salt to taste
                        black pepper to taste
     1/2  cup           butter -- unsalted
   2      tablespoons   Worcestershire sauce
   1                    juice of lemon
     1/4  cup           parsley -- chopped

Preparation:

1. Heat oil in heavy skillet; remove from heat and add flour. 2. Return to heat and cook, stirring, until roux is medium brown in color. 3. Slowly whisk in stock; bring to a boil, stirring constantly, and simmer 45 minutes. 4. Add salt and pepper. 5. Transfer sauce (there should be about 1 cup) to 2-quart saucepan; bring to a quick boil. 6. Whisk in softened butter and Worcestershire sauce; continue to whisk until butter is absorbed. 7. Add lemon juice and parsley; whisk again briefly and remove from heat. 8. This sauce should be used within 45 minutes from time it is completed. NOTE: Recipe is time-consuming but results are well worth the effort.