Combine all the ingredients for the dressing in an electric blender or food processor and process until smooth.
1 cup parsley, 1 cup mayonnaise, 1 cup sour cream, 1/4 cup chives, 1/4 cup white wine vinegar, 3 tbsp tarragon, 6 whole anchovy fillets, 1 large scallion, 1 clove garlic
The sauce should be rather thick, but you may thin it if necessary with a tablespoon or two of milk.
Pour into a glass jar with a tightly fitting lid and refrigerate for at least 3 hour to overnight.
Shake well before using.
Rub the inside of a large wooden salad bowl with the clove of garlic and discard the garlic.
1 clove garlic
Break the greens into small pieces and place them in the bowl.
1 head Boston lettuce, 1 head romaine, 1 bunch chicory
Drizzle enough of the dressing over the greens to coat them lightly and toss gently.