1. Start by cooking the egg noodles according to package instructions. Drain and set aside.
2. In a large skillet, heat olive oil over medium-high heat. Add the sliced beef and cook until browned on all sides, about 5-7 minutes. Remove the beef from the skillet and set aside.
3. In the same skillet, add the chopped onion and garlic. Sauté until the onion is translucent, about 3 minutes.
4. Add the sliced mushrooms and cook until they release their moisture and begin to brown, about 5 minutes.
5. Sprinkle the flour over the vegetables and stir well to coat. Gradually add the beef broth, stirring constantly to avoid lumps.
6. Reduce the heat to low and stir in the sour cream and Dijon mustard. Let the sauce simmer for 5 minutes until it thickens slightly.
7. Return the beef to the skillet and let it heat through in the sauce for about 2 minutes. Season with salt and pepper to taste.
8. Toss the cooked noodles with the beef and sauce until well combined. Garnish with chopped fresh parsley before serving.

Here’s a little tip from my kitchen: if you find the sauce too thick, add a splash more beef broth until you reach your desired consistency.