1) In a medium bowl, lightly toss the crab meat, celery, chives, and tarragon together.
2) In a small bowl, stir together the mayonnaise, sour cream, lemon juice, and mustard. Add the dressing to the crab meat mixture and stir until just coated. Season with salt and pepper to taste. If not using right away refrigerate until ready to serve.
3) Serve on toasted baps or on a bed of lettuce.