Begin by slicing the sirloin steak thinly against the grain and season with salt and pepper.

Heat a large skillet over medium-high heat and add oil. Sear the beef for about 2-3 minutes until browned, then set aside.

In the same skillet, add butter, then diced onion. Sauté for 3-4 minutes until softened.

Add sliced mushrooms and cook until golden, about 5 more minutes.

Stir in minced garlic, Worcestershire sauce, and Dijon mustard. Cook for 1 minute.

Pour in beef broth, scraping up browned bits, and simmer for about 5 minutes.

If desired, thicken the sauce with a flour slurry or simmer until it coats the back of a spoon.

Return the seared beef to the skillet and heat through for 3-5 minutes.

Remove from heat and stir in sour cream.

Serve the Beef Stroganoff over cooked egg noodles and garnish with chopped parsley.