With a mandoline or sharp knife, thinly slice 1 large English cucumber and 2 radishes (optional) and sprinkle with 1/2 teaspoon salt. Place in a colander and leave for 10-15 minutes. Tap the cucumbers dry and transfer to a serving bowl.
Mix the 1/2 cup of sour cream, juice of 1/2 lemon, and 1/4 freshly ground black pepper. Toss the dressing with cucumber and garnish with fresh dill. Serve immediately as an accompaniment.
This salad is best if served shortly after you make it. It's such a quick dish to make, but if you wish, you can draw water out of the cucumber ahead of time, and only mix it with the dressing right before serving.
You will have the best results with English cucumber (see tips above), but if it's not available or you grow cucumbers in your garden, by all means, use those.
For variations, you can add sliced onions, a pinch of sugar, substitute sour cream with yogurt or oil, and use chopped chives, parsley or mint.
Refrigerate any leftovers in an airtight container and use by the next day.