Prep the beef. Freeze the steak for 15 minutes to firm it up. Slice thinly across the grain. Season with salt and pepper.

Cook the noodles. Bring a large pot of salted water to a boil. Cook egg noodles according to package directions until just tender. Drain, toss with a small knob of butter, and set aside.

Sear the beef. Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Add half the beef in a single layer and sear 1 to 2 minutes per side until browned but not fully cooked. Transfer to a plate. Repeat with remaining beef and another splash of oil if needed.

Sauté the vegetables. Lower heat to medium. Add butter to the same skillet. Stir in onions and cook 3 to 4 minutes until softened. Add mushrooms and a pinch of salt. Cook, stirring occasionally, until their moisture evaporates and they brown, about 6 to 8 minutes. Add garlic and cook 30 seconds, until fragrant.

Build the sauce. Sprinkle flour over the mushroom mixture and stir for 30 seconds. Slowly pour in beef broth while stirring, scraping up browned bits from the pan. Add Worcestershire sauce and Dijon. Simmer 2 to 3 minutes until slightly thickened.

Finish with sour cream. Turn heat to low. Stir in sour cream until smooth. If the sauce seems too thick, add a splash of water or more broth. Taste and adjust salt and pepper. Add a small squeeze of lemon juice if you want extra brightness.

Combine and warm through. Return the seared beef and any juices to the pan. Add the cooked noodles and toss to coat evenly. Warm for 1 to 2 minutes, just until the beef is cooked to your liking and the noodles are glossy.

Serve. Top with chopped parsley and freshly cracked pepper. Serve hot.