Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   1                    egg yolk
   2      tablespoons   tarragon vinegar
     1/2  teaspoon      hot brown mustard
   1      pinch         cayenne pepper
     1/2  teaspoon      salt
     1/2  cup           vegetable oil

Preparation:

In a medium bowl, whisk together the yolk, vinegar, mustard, salt and pepper until smooth. Slowly add the oil, beating continuously, until absorbed and thick. Taste and adjust seasoning if needed. Stir before serving, as sauce may separate.