Add the mayonnaise, sour cream, buttermilk, cilantro, lime juice, lime zest (if using), garlic, dill, chives, onion powder, garlic powder, salt, pepper, and cumin to a blender or food processor.
Blend for 30–60 seconds until smooth and creamy.
Taste the dressing and adjust the seasoning with more salt, lime juice, or buttermilk if needed.
Transfer the dressing to an airtight jar or container.
Refrigerate and let it rest for 30 minutes to allow the flavors to develop.
Stir before serving and enjoy over salads, tacos, burrito bowls, grilled chicken, vegetables, or as a dip.