Thinly slice the English cucumbers into 1/8-inch rounds and the red onion into half-moons. I find that slicing the cucumber into thinner rounds than typical salads helps them absorb the creamy dressing more evenly. Place the sliced vegetables in a large mixing bowl and set aside.

In a separate bowl, whisk together the sour cream, mayonnaise, white vinegar, sugar, salt, garlic powder, and freshly cracked black pepper until smooth and well combined. The vinegar will slightly thin the mixture while adding brightness, and the sugar balances the acidity beautifully. Fold in the fresh dill gently at the end to preserve its vibrant color and delicate flavor.

Pour the creamy dressing from Step 2 over the prepared cucumbers and onions, then gently toss until all the vegetables are evenly coated. Transfer to a serving dish or storage container and refrigerate for at least 1 hour. I like to chill this salad ahead of time—the flavors meld together and become more cohesive after sitting in the cold, creating a more flavorful dish than if served immediately.

Remove the salad from the refrigerator and give it a gentle stir. Taste and adjust seasoning as needed—you may want to add a pinch more salt, pepper, or a small amount of fresh dill if desired. Serve chilled as a refreshing side dish.