Bring a large pot of salted water to a boil. Add the wide egg noodles and cook to just tender, about 7–8 minutes. Drain and set aside.

Heat a large skillet over medium-high heat. Add the butter. When foaming, add the ground beef and break it apart with a wooden spoon. Cook until well-browned and no pink remains, about 5–6 minutes. Drain excess fat if the pan is very oily.

Push the beef to one side of the skillet. Add the chopped onion and sliced mushrooms to the empty side. Sauté until the onion is soft and the mushrooms are golden, 4–5 minutes. Stir in minced garlic and cook 30 seconds until fragrant.

Sprinkle flour over the meat and vegetables. Stir to coat evenly and cook 1 minute to remove the raw flour taste.

Slowly pour in the beef broth while stirring to avoid lumps. Add Worcestershire sauce, Dijon (if using), salt, and pepper. Bring to a gentle simmer and cook 3–4 minutes until the sauce thickens slightly.

In a small bowl, whisk the sour cream with a ladle of hot sauce from the pan to temper it. Reduce heat to low and slowly stir the tempered sour cream into the skillet. Simmer 2–3 minutes, stirring constantly, until the sauce is smooth and creamy. Adjust seasoning to taste.

Fold in the cooked egg noodles until they’re well-coated. If using frozen peas, stir them in now and heat through for 1–2 minutes.

Finish with chopped fresh parsley and serve immediately.