Heat olive oil in a large skillet over medium-high heat.
Season the beef slices with salt and pepper.
Sear the beef in batches until just browned and set aside.
In the same skillet, add a bit of butter.
Stir in sliced onions and cook until they become soft.
Add minced garlic and sliced mushrooms, cooking until the mushrooms are golden.
Return the beef to the skillet.
Pour in the beef stock and let it simmer, allowing the flavors to meld.
Stir occasionally for about 5 minutes.
Add sour cream and Dijon mustard, stirring until the mixture is well combined and creamy.
Adjust seasoning to your taste.
Let it cook for about 5 more minutes on low heat.
Prepare the egg noodles according to package instructions.
Serve the beef stroganoff over the cooked noodles and enjoy!