Whisk together the mayonnaise and buttermilk in a medium mixing bowl.
Add the seasonings. Whisk again until the herbs and seasonings are thoroughly combined.
Transfer the dressing to an airtight container with a lid and store it in the refrigerator.
Video
Notes
For a thicker dressing, only use one cup of buttermilk. For a thinner dressing, use two. The dressing will thicken up as it chills.If stored properly, buttermilk ranch dressing will last up to two weeks.