In a pot, sauté the onion. Add cleaned and sliced mushrooms and drizzle them with lemon juice. Cook for several minutes. Pour in water with 2 cubes of broth and cook. Next, add the diced potatoes and caraway seeds in the soup. When the potatoes are almost soft, mix in a bowl water, one tablespoon of all purpose flour, a bit of heavy cream, and 3 tablespoons of sour cream. Stir everything well and pour into the soup. Cook for a while and finally season with soy sauce, salt, and lemon juice.