01 - Season the sliced beef thoroughly with salt and pepper on all sides.
02 - Heat 1 tbsp olive oil in a large skillet over medium-high heat. Sear the beef in batches for 1-2 minutes per side until browned but not cooked through. Remove and set aside on a plate.
03 - Reduce heat to medium. Add the remaining olive oil and butter to the same skillet. Sauté the onions for 2-3 minutes until softened, then add mushrooms. Cook until mushrooms are browned and any liquid has evaporated, about 5 minutes.
04 - Stir in the minced garlic and cook for 1 minute until fragrant.
05 - Sprinkle the flour over the vegetables, stirring well to coat everything evenly. Cook for 1 minute to remove the raw flour taste.
06 - Gradually pour in the beef broth while stirring constantly, scraping up any browned bits from the bottom of the pan. Add Dijon mustard and Worcestershire sauce. Stir until the sauce begins to thicken, about 3 minutes.
07 - Reduce the heat to low. Return the beef and any accumulated juices back to the pan. Simmer gently for 2-3 minutes until the beef is just cooked through.
08 - Remove the skillet from heat completely. Stir in the sour cream until the sauce is smooth and creamy. Adjust seasoning with additional salt and pepper as needed.
09 - Serve the stroganoff hot over cooked egg noodles. Garnish with chopped fresh parsley.