In a medium bowl, combine the mayonnaise, sour cream, buttermilk, kosher salt, black pepper, garlic powder, onion powder, dried chives, dried dill, and dried parsley.
Whisk with a hand whisk until smooth.
Serve immediately, or cover and refrigerate the dressing for an hour to allow the flavors to meld.
Video
Notes
This dressing is excellent right after you've mixed it, so you can definitely serve it right away. But if you let it rest in the fridge, covered, for an hour or so, allowing the flavors to meld, it gets even better. Just remember to give it another whisk before using it.
You can make this dressing with fresh herbs instead of dried ones. You can use fresh parsley, chives, dill, and minced garlic. If opting for fresh herbs, mince them finely and use a tablespoon of each.
The dressing as made here is quite thick, so if you'd like it thinner for a salad, add a bit more buttermilk - start with two extra tablespoons.
You can store this dressing in an airtight container in the fridge for up to a week. Stir it each time you use it, and add a little more buttermilk if it becomes too thick. I don't recommend freezing this dressing.