Season the beef strips generously with salt and black pepper. Heat the olive oil in a large skillet over medium-high heat until shimmering.

Add the seasoned beef to the hot skillet in a single layer, working in batches if necessary so you don't overcrowd the pan. Sear the meat for 1 to 2 minutes per side until beautifully browned, then transfer it to a plate and set aside.

In the same skillet, lower the heat to medium and melt the butter. Add the sliced mushrooms and chopped onions, cooking for 5 to 7 minutes until the onions are soft and the mushrooms are golden brown.

Stir in the minced garlic and cook for about 30 seconds until fragrant. Sprinkle the flour over the mushroom mixture and stir constantly for 1 minute to cook out the raw flour taste.

Gradually whisk in the beef broth, making sure to scrape up any browned bits from the bottom of the pan. Stir in the Dijon mustard and Worcestershire sauce, then bring the mixture to a gentle simmer.

Allow the sauce to simmer for 3 to 5 minutes until it has thickened enough to coat the back of a spoon. Meanwhile, bring a large pot of salted water to a boil and cook the egg noodles according to the package directions.

Reduce the skillet heat to low and stir in the sour cream until completely smooth and heated through, being careful not to let the sauce boil. Return the browned beef strips and any resting juices to the pan, stirring gently to combine.

Taste the stroganoff and adjust the seasoning with more salt and pepper if needed. Serve the creamy beef mixture hot over the freshly cooked egg noodles, garnished with a sprinkle of chopped fresh parsley.