Prepare the beef by patting the beef sirloin steak dry with paper towels, then slicing it into thin strips against the grain if not already sliced.

Season the sliced beef with about half of the fine sea salt and half of the freshly ground black pepper, tossing to coat evenly.

Sprinkle the all-purpose flour over the seasoned beef strips and toss again until the beef is lightly and evenly coated in flour.

Heat the olive oil in a large, heavy-bottomed skillet over medium-high heat until shimmering.

Add half of the floured beef strips to the hot skillet in a single layer, searing for 1–2 minutes per side until browned but not fully cooked through, then transfer to a plate.

Repeat with the remaining beef strips, adding a little more olive oil if needed, and transfer the second batch of browned beef to the same plate.

Reduce the heat to medium and add the unsalted butter to the same skillet, allowing it to melt and loosen any browned bits from the bottom.

Add the thinly sliced yellow onion to the skillet and cook, stirring often, for 5–7 minutes until the onion is soft and lightly golden.

Stir in the minced garlic and cook for 30 seconds to 1 minute, just until fragrant, being careful not to let it brown.

Pour in the Worcestershire sauce and Dijon mustard, stirring to coat the onions and garlic and to deglaze the skillet.

Slowly add the low-sodium beef broth while stirring, scraping up any browned bits from the bottom of the skillet to build flavor.

Sprinkle in the paprika and the remaining fine sea salt and freshly ground black pepper, then bring the mixture to a gentle simmer.

Reduce the heat to medium-low and let the sauce simmer for about 5 minutes, allowing it to slightly thicken and the flavors to meld.

Pour in the heavy cream, stirring well to combine it with the onion and broth mixture until the sauce looks smooth and creamy.

Return the browned beef strips and any accumulated juices on the plate back into the skillet, stirring to coat the beef in the creamy sauce.

Simmer the beef gently in the sauce for 5–8 minutes over low to medium-low heat, just until the beef is cooked through and tender.

Place the sour cream in a small bowl and whisk in a few spoonfuls of the hot sauce from the skillet to gently warm the sour cream and prevent curdling.

Stir the warmed sour cream mixture into the skillet, mixing until fully incorporated and the sauce is velvety and smooth. Do not let it boil once the sour cream has been added.

Taste the beef stroganoff and adjust the seasoning with a little more salt or pepper if needed.

Just before serving, sprinkle the chopped fresh parsley over the beef stroganoff for a fresh, bright finish.

Serve the hot beef stroganoff spooned generously over cooked wide egg noodles on individual plates or in shallow bowls.