Place the anchovies, garlic, parsley, basil, tarragon, scallions, lemon juice, vinegar, mayonnaise, sour cream, and mustard into a food processor or blender. Process until fairly smooth.
Notes
Substitute 1 tablespoon of rinsed and drained capers for the anchovies for a vegetarian version.
This salad will last for 5 days in the fridge in a tightly sealed container.