Combine the cucumbers and purple onion in a large bowl and set aside.
In another bowl, whisk together the sour cream, mayo, vinegar, sugar, dill, salt and black pepper. Pour over cucumbers and toss to combine.
Cover and chill cucumber salad in fridge for two hours* to let flavors blend. Toss before serving and garnish with extra dill and pepper. Enjoy!
Notes
*You don't have to chill the cucumber salad for the full 2 hours, it just helps to develop the flavors a little more. Feel free to serve right away if desired.