Cook the Egg Noodles: Bring a large pot of salted water to a boil. Cook egg noodles according to package instructions until al dente. Drain and toss with butter if desired. Set aside.

Prepare the Beef: Heat 1 tbsp olive oil in a large skillet or sauté pan over medium-high heat. Season beef slices with salt, pepper, and paprika. Sear beef in batches for 2–3 minutes per side until browned but not fully cooked. Remove and set aside.

Sauté Vegetables: In the same skillet, add remaining olive oil or butter. Sauté onions for 2–3 minutes until translucent. Add garlic and cook 30 seconds. Add mushrooms and cook until they release moisture and turn golden brown.

Make the Sauce: Sprinkle flour over mushrooms (if using) and stir to combine. Pour in beef broth, Worcestershire sauce, and Dijon mustard. Simmer for 3–5 minutes until slightly thickened.

Combine Beef and Sauce: Lower heat and return beef to the skillet. Stir to coat in sauce. Remove from heat and gently fold in sour cream. Adjust seasoning with salt and pepper.

Serve: Spoon the creamy beef mixture over cooked egg noodles. Garnish with fresh parsley if desired.