In a large pot or Dutch oven, heat the olive oil over medium-high heat. Carefully add the thinly sliced beef sirloin, seasoning it generously with salt and freshly ground black pepper. Sauté for about 3-4 minutes, stirring occasionally, until the beef is browned all over. Once browned, remove the beef from the pot, transferring it onto a plate and setting it aside.
Without wiping the pot, add the finely chopped onion and minced garlic. Sauté for 2-3 minutes, or until the onion becomes soft and translucent, stirring frequently to avoid burning the garlic.
Incorporate the sliced mushrooms into the pot, stirring to combine. Cook for about 5 minutes, until the mushrooms have softened and released their juices.
Carefully pour in the low-sodium beef broth, followed by the Worcestershire sauce and Dijon mustard. Stir the mixture well and bring it to a gentle boil over medium heat.
Add the egg noodles to the boiling broth, ensuring they are fully submerged. Stir gently, then cover the pot. Reduce the heat and let it simmer for about 10-12 minutes, or until the noodles are cooked al dente, stirring occasionally to prevent sticking.
Once the noodles are cooked, reduce the heat to low and return the browned beef to the pot. Stir in the sour cream until the mixture is well combined and creamy. Allow it to cook for an additional 2-3 minutes until heated through, but do not let it boil.
Taste the dish and adjust the seasoning with additional salt and freshly ground black pepper as desired.
Serve your creamy beef stroganoff hot, garnishing each bowl with a sprinkle of chopped fresh parsley for a pop of color and freshness.