3/4 c Watercress,packed,chopped

3/4 c Unflavored nonfat yogurt

3/4 c Mayonnaise

1 tb Lemon juice

1/2 ts Dried tarragon leaves

1 Garlic clove

2 ts Fish sauce or anchovy paste

In a blender or food processor, combine watercress, yogurt, mayonnaise, lemon juice, tarragon, and garlic; whirl until smooth. Add fish sauce to taste; whirl to blend. (If sauce is made ahead, cover and chill up to a day.) Makes about 1 1/2 cups.