Cut the onion into thin slices using a sharp knife or mandoline. Wash the cucumbers, then cut them into thin slices also and pat them dry with paper towels to absorb any excess moisture.

In a medium mixing bowl, combine the sour cream, white vinegar, minced fresh dill, granulated sugar, salt, and garlic powder. Stir until combined.

Add the sliced cucumbers and red onion and toss gently to coat.

Garnish with additional fresh dill and fresh black pepper as desired. Serve immediately or cover and chill before serving. Store leftovers, covered, in the refrigerator for up to 3 days.