Kapros-tejfolos gombaleves - Hungarian mushroom soup

4 tablespoons unsalted butter
2 cups chopped onions
1 pound fresh mushrooms, sliced
1 teaspoon dried dill weed
3 teaspoons paprika
1 tablespoon soy sauce
2 cups vegetable broth
1 cup milk
3 tablespoons unbleached all-purpose flour
1 teaspoon salt
ground black pepper to taste
1 teaspoon lemon juice
1/2 cup sour cream

Melt the butter in a large pot over medium heat. Saute the onions in the butter for 5 minutes. Add the mushrooms and saute for 5 more minutes. Stir in the dill, paprika, soy sauce and broth, bring to a boil. 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 for 15 more minutes, stirring occasionally.
Finally, stir in the salt, ground black pepper and sour cream. Mix together and allow to heat through over low heat, about 3 to 5 minutes. Add lemon juice. Do not boil. Serve immediately.