Preheat oven to 200℃/400℉. Wrap your potatoes in aluminum foil and bake them until soft.
Meanwhile finely chop onion, radishes, chives and dill and put it in a bowl, sprinkle with salt, pepper and sugar, mix it well and put it in the fridge for at least 30 min, but you can even let it sit for a few hours.
Then add cheese and sour cream, mix it well. It should have the consistency of soft cream cheese. Chill very well.
Take potatoes out of the oven, cut them in half, you can add some butter inside. Put a big portion of cold gzik in the middle and enjoy!