01 - Bring a large pot of salted water to a boil. Cook egg noodles according to package instructions. Drain, toss with a little butter, and set aside.
02 - Season beef strips with salt and freshly ground black pepper.
03 - In a large skillet over medium-high heat, melt 1 tablespoon of butter. Add beef in batches and sear quickly until browned, about 1 minute per side. Transfer beef to a plate and cover loosely.
04 - Add remaining butter to the skillet. Sauté onions for 2 to 3 minutes until softened. Add garlic and mushrooms, cooking until mushrooms are browned and moisture has evaporated, about 5 to 7 minutes.
05 - Sprinkle flour over the vegetables, stir well, and cook for 1 minute to remove raw flour taste.
06 - Gradually pour in beef broth while stirring to deglaze the pan. Add Worcestershire sauce and Dijon mustard. Bring mixture to a simmer.
07 - Reduce heat to low. Stir in sour cream until the sauce is smooth and warmed through. Avoid boiling to prevent curdling.
08 - Return beef and any accumulated juices to the pan. Simmer gently for 2 to 3 minutes until beef is cooked through. Taste and adjust seasoning as needed.
09 - Plate egg noodles and spoon stroganoff over them. Garnish with chopped fresh parsley.