01 - In a bowl, combine beef strips with all-purpose flour, salt, and black pepper. Toss until evenly coated.
02 - Heat 1 tbsp butter and olive oil in a large skillet over medium-high heat. Sear beef strips in batches for 1 to 2 minutes until browned. Remove beef and set aside.
03 - Reduce heat to medium. Add remaining butter to the skillet. Sauté finely chopped onions for 3 minutes until translucent. Add minced garlic and cook for 30 seconds.
04 - Add sliced mushrooms and cook for 5 to 7 minutes until browned and moisture evaporates.
05 - Stir in tomato paste and Dijon mustard. Cook for 1 minute to combine flavors.
06 - Pour in beef broth and Worcestershire sauce, scraping up browned bits from the pan. Bring to a simmer and cook for 3 minutes.
07 - Return the seared beef and its juices to the skillet. Simmer gently for 3 to 4 minutes to meld flavors.
08 - Reduce heat to low. Stir in sour cream until smooth and warmed through without boiling.
09 - Plate over cooked egg noodles or rice, garnishing with chopped fresh parsley if desired.