Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   2      tablespoons   butter
   1      tablespoon    flour
   2      cups          cold water
     1/2  teaspoon      salt
   1                    egg yolk
   2      tablespoons   capers

Preparation:

In small, heavy saucepan, melt 1 tablespoon butter. Stir in flour. Add cold water and salt. Stir in egg yolk and cook over low flame, stirring constantly. Bring to boiling point but do not boil. Take pan off fire and add remaining butter and capers. Stir until well blended. This sauce is served with boiled fish. Recipe Source: THE ART OF FRENCH COOKING by Fernande Garvin