1Bring vegetable stock to boil and add potatoes. After 10 minutes add sliced mushrooms, caraway seeds and salt.
2Whisk flour into milk and cream and thru strainer slowly, while stirring it, pour into the boiling soup (you will see it thicken). On low heat boil for 5 more minutes, potatoes should be now tender.
3Add more salt, chopped dill and take off the heat. Finish the taste with vinegar.
4Before serving, put small cube of butter on top and slices of hard boiled egg.