Bring a small pot of salted water to a boil and cook the egg noodles according to package directions until al dente, then drain and set aside.
While noodles cook, slice the beef sirloin into thin strips and season with half of the sea salt and black pepper.
Heat the ghee in a large skillet over medium-high heat. Add the beef strips in a single layer and sear until browned, about 1-2 minutes per side. Remove beef from the pan and set aside.
In the same skillet, add the diced onion and sliced mushrooms. Sauté for 5-6 minutes until the mushrooms have released their moisture and turned golden brown.
Add the minced garlic to the skillet and cook for 30 seconds until fragrant.
Pour in the beef broth to deglaze the pan, scraping up any browned bits from the bottom. Simmer for 2 minutes until the liquid reduces slightly.
Reduce the heat to low. Stir in the Greek yogurt, Dijon mustard, and the remaining salt and pepper until the sauce is smooth and creamy.
Return the beef and any accumulated juices to the skillet, tossing to coat in the sauce for 1 minute until heated through.
Serve the beef and mushroom mixture over the cooked egg noodles and garnish with freshly chopped parsley.