Sauté onions and mushrooms in butter over medium heat until softened, about 5–7 minutes.
Add garlic and cook 30 seconds, then push veggies to the side and brown the ground beef; drain excess fat if needed.
Sprinkle flour over mixture, stir 1 minute, then slowly add beef broth while stirring to avoid lumps.
Simmer 3–5 minutes until slightly thickened, then remove from heat and stir in sour cream, Dijon, and Worcestershire; season to taste.
Toss with cooked egg noodles and heat gently until warm. Garnish with parsley and serve.