In a large pot, melt the butter over medium heat. Add the chopped onions and sliced mushrooms, cooking and stirring for about 8 minutes until the onions soften and become translucent.
Pour in the broth, white wine, thyme, dill, paprika, Worcestershire sauce, and salt. Bring the mixture to a boil, then reduce the heat to a low simmer for about 10 minutes.
Whisk the flour into the milk until smooth, then add to the soup and let it cook for an additional 10 minutes, stirring occasionally.
Stir in the sour cream and optional lemon juice until well combined, then serve hot garnished with fresh parsley if desired.