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

While the noodles cook, pat the beef sirloin strips dry with paper towels. Season the beef with about half of the kosher salt and half of the freshly ground black pepper, then sprinkle the all-purpose flour over the beef and toss to coat evenly.

Heat the olive oil in a large, deep skillet over medium-high heat. Add the floured beef strips in a single layer, working in batches if necessary, and sear for 1 to 2 minutes per side until browned but not fully cooked through. Transfer the browned beef to a plate and set aside.

Reduce the heat to medium and add the unsalted butter to the same skillet. Once melted, add the thinly sliced yellow onion and cook, stirring often, for about 3 to 4 minutes until it begins to soften and turn translucent.

Add the sliced cremini mushrooms to the skillet with the onion. Cook, stirring occasionally, for 5 to 6 minutes until the mushrooms release their moisture and turn golden in spots.

Stir in the minced garlic and cook for about 30 seconds until fragrant, then sprinkle in the sweet paprika and the remaining kosher salt and freshly ground black pepper, stirring to coat the vegetables evenly in the seasoning.

Add the Dijon mustard, beef broth, and Worcestershire sauce to the skillet. Stir well, scraping up any browned bits from the bottom of the pan, and bring the mixture to a gentle simmer.

Return the browned beef strips and any accumulated juices to the skillet. Reduce the heat to medium-low and simmer for 4 to 5 minutes, or until the beef is just cooked through and the sauce has slightly thickened.

Turn the heat to low. Stir the sour cream into the skillet until fully blended and the sauce is smooth and creamy. Do not let the sauce boil once the sour cream is added to prevent curdling.

Add the cooked egg noodles to the skillet with the creamy beef mixture. Gently toss until the noodles are well coated in the sauce and everything is evenly combined and heated through.

Sprinkle the chopped fresh parsley over the beef stroganoff and noodles. Taste and adjust seasoning with additional salt and pepper if desired, then serve warm.