In a medium bowl, combine cucumber, red onion, dill and chives.
In a separate bowl, whisk together buttermilk, mayonnaise, sugar, vinegar, salt and pepper. Pour the dressing over the cucumber mixture and toss to combine.
Cover and refrigerate for about 15-30 minutes or up to 4 hours.
Swap out the mayonnaise for sour cream or plain Greek yogurt. The dressing will have a more tangy, slightly less salty flavor, but it will still be good.
If available, include additional fresh herbs in the salad. Parsley, basil, thyme and oregano would all be delicious.
For a more mild taste, omit the red onion and just use the fresh chives. You can also substitute with sweet Vidalia onion if you prefer.
Include sliced radishes for extra color and a zesty bite.
To feed a larger group, double all of the ingredients.
Use a mandoline slicer to quickly cut the cucumbers into equal rounds. Make sure that you use the wider setting on the mandoline so that your cucumbers are not paper-thin. The thicker rounds stand up to the dressing and stay crisp for longer.
Use whole buttermilk rather than low-fat buttermilk, since the whole buttermilk has a much thicker, richer texture and flavor. Be sure to shake the bottle well before using it, too!
If time allows, let the cucumbers sit and marinate with the other ingredients for about 15-30 minutes before serving. Do not prepare the salad too far in advance, though. It's best when enjoyed within about 4 hours so that the cucumbers don't get soggy.