Slice the cucumbers into thin rounds, about 1/8-inch thick.
Place cucumber slices in a colander and sprinkle with 1 teaspoon salt. Toss gently and let sit for 10 minutes to draw out excess moisture.
Rinse the cucumbers under cold water and pat dry thoroughly with paper towels or a clean kitchen towel.
In a medium bowl, whisk together mayonnaise, sour cream, fresh dill, black pepper, and 1/4 teaspoon salt until smooth.
Add the dried cucumber slices and optional red onion to the dressing. Gently toss until all pieces are evenly coated.
Transfer the salad to a serving bowl, cover, and refrigerate for at least 30 minutes before serving to allow flavors to meld.
Give the salad a quick stir before serving. Adjust seasoning with additional salt or pepper if desired.
