Peel and halve the cucumbers lengthwise. If necessary, scoop out the seeds and slice thinly crosswise. Place in large bowl and add sliced onions.
In separate bowl, whisk together sour cream, cider vinegar, sugar and dill until sugar is dissolved. Season with a little salt and pepper.
Add dressing to cucumber and onions, toss well to combine. Cover with plastic wrap and refrigerate for at least 1 hour or longer, stirring occasionally. Serve and enjoy!
Notes
It's totally fine not to peel or seed the cucumbers, it's a personal preference.
Regular white vinegar can be substituted for the apple cider vinegar.
Fresh dill can be used instead of dry, you'll need more of it, adjust to taste.