In a blender or food processor, add the herbs, garlic, and capers, then add mayonnaise, sour cream, and lemon juice.
Blend until herbs are finely chopped and dressing is smooth. If a thinner consistency is desired, blend in a small amount of water. Taste dressing and add salt and pepper as needed, then pulse a few times to mix. Store in the refrigerator for up to 7 days.