Prepare the Beef. Slice the beef sirloin into thin strips against the grain. This ensures tenderness. Toss the strips in the flour until evenly coated — this helps them brown nicely and thickens the sauce later. Set aside.

Cook the Noodles: In a medium pot, bring salted water to a boil. Add the egg noodles and cook according to package directions until tender. Drain, toss with a drizzle of olive oil to prevent sticking, and set aside.

Sauté the Vegetables: Heat olive oil in a large skillet over medium-high heat. Add the sliced onions and mushrooms, stirring occasionally until softened and golden brown, about 6–7 minutes. Remove them from the pan and set aside.

Brown the Beef: Without cleaning the skillet, melt the butter over medium-high heat. Add the floured beef strips in batches, making sure not to overcrowd the pan. Sear each side for about 1–2 minutes until lightly browned. The goal is to get a nice crust without overcooking.

Deglaze and Build the Sauce: Return the onions and mushrooms to the skillet with the browned beef. Pour in the beef broth and Worcestershire sauce, scraping up any browned bits from the bottom — those bits are pure flavor! Let the mixture simmer gently for 2–3 minutes until it begins to thicken.

Add the Creamy Components: Lower the heat to medium-low. Stir in the sour cream and Dijon mustard. Mix until the sauce turns smooth and creamy. Be careful not to let it boil after adding the sour cream, as it could curdle.

Season and Combine: Add salt and black pepper to taste. Stir in the cooked egg noodles until they’re fully coated in the sauce. Let everything warm together for about a minute.

Serve and Enjoy: Serve hot, garnished with fresh parsley if desired. Pair it with a side salad, roasted vegetables, or garlic bread for a complete meal.