01 - Season beef strips evenly with salt and pepper on all sides.
02 - Heat 1 tbsp olive oil and 1 tbsp butter in a large skillet over medium-high heat. Add beef in batches, searing quickly for 1-2 minutes per side until browned but still pink inside. Transfer to a plate and reserve juices.
03 - In the same skillet, add remaining olive oil and butter. Sauté onions until softened and translucent, about 3 minutes. Add garlic and cook for 1 minute until fragrant.
04 - Add sliced mushrooms to the skillet. Sauté until browned and all liquid has evaporated, approximately 5 minutes.
05 - Sprinkle flour evenly over vegetables, stirring constantly to coat. Cook for 1 minute to remove raw flour taste.
06 - Gradually pour in beef broth while whisking constantly to prevent lumps. Add Worcestershire sauce and Dijon mustard. Bring to a gentle simmer and cook for 5 minutes, stirring occasionally, until sauce slightly thickens.
07 - While sauce simmers, cook egg noodles in salted boiling water according to package directions until al dente. Drain thoroughly and set aside.
08 - Reduce heat to low. Return beef and accumulated juices to the skillet. Warm gently for 2-3 minutes until heated through. Do not boil to prevent toughening.
09 - Remove skillet from heat entirely. Stir in sour cream and half the parsley until sauce is smooth and creamy.
10 - Plate stroganoff over cooked egg noodles. Sprinkle with remaining parsley and serve immediately.