1/4 cup white wine vinegar
1/4 cup freshly squeezed lemon juice
1/8 teaspoon salt
1/2 cup heavy cream
1 large egg, well beaten
1 tablespoon chopped fresh chives
1 tablespoon chopped fresh tarragon
6 cups diced cooked chicken
1 to 2 tablespoons fresh chives, cut into 1-inch lengths (optional)
1 to 2 tablespoons fresh tarragon leaves (optional)
2 to 3 teaspoons grated lemon zest (optional)
4 cups trimmed watercress, washed and dried
4 cups Belgian endive or trimmed Bibb or Boston lettuce, washed and dried
To make the dressing, bring the vinegar, lemon juice, and salt to a boil in a medium saucepan. Reduce the heat to low. Add the cream, then the egg. Cook over low heat, stirring constantly, for 2 to 5 minutes, or until the mixture thickens and coats the back of a wooden spoon. Do not let the mixture overheat or it will curdle. Add the chives and tarragon and cool to room temperature.
Place the chicken in a bowl and toss it with 1/2 to 2/3 cup of the dressing, or enough to coat the chicken lightly. Taste, adding salt and pepper, and herbs to taste, if you are using them.
Line a platter or individual plates with the watercress and endive or lettuce leaves. Mound the chicken salad on top and garnish with the remaining herbs and lemon zest, if you like.
Serve cool (not cold) or at room temperature and pass any remaining dressing at the table.
Note: The dressing can be kept, covered, in the refrigerator for up to 2 weeks. Sliced tomatoes, chopped bell peppers, diced celery, or hard-boiled eggs can be added to the chicken.
4 to 6 servings