Peel the cucumbers, cut them in half lengthwise and scrape out the seeds with a spoon. Cut the cucumbers into small pieces. Peel, wash and chop the potatoes. Peel and chop the onion.
Bring 1 l water, onion, cucumber and potatoes to the boil. Add the stock and simmer for 15-20 minutes. Finally add milk to the soup.
Heat the oil in a pan. Fry the tartar in it for about 5 minutes until crumbly. Wash the dill, shake dry and cut the flags into small pieces. Crumble the feta.
Puree the soup briefly, season to taste with salt and pepper and serve. Spread minced meat and feta over it and sprinkle with dill.