01 - In a bowl, toss the beef strips with flour, salt, and black pepper.
02 - Heat 1 tbsp butter and olive oil in a large skillet over medium-high heat. Sear the beef strips in batches for 1 to 2 minutes until browned. Remove and set aside.
03 - Reduce heat to medium and add remaining butter to the skillet. Sauté chopped onions for 3 minutes until translucent, then add minced garlic and cook for 30 seconds.
04 - Add sliced mushrooms and cook for 5 to 7 minutes until browned and moisture has evaporated.
05 - Stir in tomato paste and Dijon mustard, cooking for 1 minute.
06 - Pour in beef broth and Worcestershire sauce, scraping up any browned bits. Bring to a simmer and cook for 3 minutes.
07 - Return beef and any accumulated juices to the pan. Simmer gently for 3 to 4 minutes.
08 - Lower heat to low and stir in sour cream until smooth and heated through, taking care not to boil.
09 - Plate beef stroganoff over egg noodles or rice. Garnish with chopped fresh parsley if desired.