Throw everything into a blender, and blend until smooth, about one minute.
Taste the dressing on a piece of lettuce, and adjust the seasonings as needed.
You can keep this sauce covered in the fridge for up to 10 days.
You can use fresh or bottled lime juice.
Notes
I like to make this first and let it sit in the fridge while I get the rest of dinner ready. It gives the flavors a little time to mix and mingle.
The dressing is relatively thin, but that means it covers everything well. If you want it a bit thicker, omit the buttermilk, or add just enough to reach the desired consistency.
Miracle Whip or salad dressing can't be used in place of the mayonnaise.