In a skillet over medium-high heat, cook bacon and onion in butter until the onions are translucent and the bacon has rendered its fat.
Stir in the sliced mushrooms and cook for about 5 minutes, stirring constantly, until tender.
Mix in the tomato paste and broth, then stir in paprika, salt, and pepper. Bring to a boil, then reduce heat and simmer gently for about 5 minutes.
If the sauce is too thin, slowly stir in just enough cornstarch slurry (cornstarch mixed with water) until the desired consistency is reached.
Stir in chopped parsley and sour cream. Taste and adjust seasoning with additional salt and pepper if needed.
