Bring a large pot of salted water to a boil. Add the wide egg noodles and cook according to the package directions until just tender. Drain well and set aside.

While the noodles cook, pat the beef sirloin strips dry with paper towels and season lightly with a pinch of the salt and black pepper.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add half of the beef strips in a single layer and sear for 1–2 minutes per side, just until browned but not fully cooked through. Transfer the browned beef to a plate and repeat with the remaining 1 tablespoon of olive oil and the rest of the beef.

Reduce the heat to medium and add the unsalted butter to the same skillet. Once melted, add the finely sliced yellow onion and cook, stirring often, for 3–4 minutes until softened and lightly golden.

Add the sliced cremini mushrooms to the skillet with the onions. Cook for 5–6 minutes, stirring occasionally, until the mushrooms release their moisture and become nicely browned.

Stir in the minced garlic, the remaining salt, and the black pepper. Cook for about 30 seconds until the garlic is fragrant, stirring constantly to keep it from burning.

Sprinkle the all-purpose flour evenly over the onion and mushroom mixture. Stir well to coat the vegetables, and cook for 1–2 minutes to remove the raw flour taste.

Slowly pour in the beef broth while stirring, making sure to scrape up any browned bits from the bottom of the skillet. Add the Worcestershire sauce and Dijon mustard, and continue stirring until the sauce is smooth.

Bring the sauce to a gentle simmer and cook for 3–4 minutes, stirring occasionally, until it thickens slightly to a creamy consistency.

Return the seared beef strips and any accumulated juices on the plate back into the skillet. Stir to coat the beef in the sauce, and simmer on low heat for 3–4 minutes, just until the beef is cooked through and tender.

Reduce the heat to low and stir in the sour cream until fully incorporated, creating a smooth and creamy stroganoff sauce. Do not let the sauce boil after adding the sour cream to prevent curdling.

Add the cooked egg noodles to the skillet with the beef stroganoff and gently toss until the noodles are well coated with the sauce.

Taste and adjust seasoning with additional salt and black pepper if needed. Sprinkle the chopped fresh parsley over the top for a fresh finish.

Serve the beef stroganoff with egg noodles hot, spooning extra sauce over each portion and garnishing with a little more parsley if desired.