Melt the butter in a large pot over med heat. Saute the onions in the butter for 5 minutes. Add the mushroom and saute for 5 more minutes. Stir in the dill, paprika, soy sauce and chicken broth. Reduce heat to low, cover and simmer for 15 minutes.
In a separate small bowl, whisk the milk and flour together. Pour this into the soup and stir well to blend. Cover and simmer 15 more minutes, stirring occasionally.
Finally, stir in the salt, pepper, lemon juice, parsley and sour cream. Mix together and allow to heat through over low heat, about 3 to 5 minutes. Do not boil. Serve immediately. Even better the next day!