Cook the Beef: Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Season the beef strips with salt and black pepper. Add the beef to the skillet and sear for about 2 minutes on each side until browned. Remove the beef from the skillet and set aside.

Sauté Onions and Garlic: In the same skillet, add the remaining 1 tablespoon of olive oil. Add the chopped onion and minced garlic. Sauté for 2-3 minutes until the onion becomes translucent and fragrant.

Add Mushrooms: Add the sliced mushrooms to the skillet. Cook for about 5 minutes until the mushrooms are soft and have released their moisture.

Prepare the Sauce: Sprinkle the flour over the mushroom mixture. Stir well to combine and cook for 1 minute to eliminate the raw flour taste. Gradually pour in the beef broth while stirring to prevent lumps. Let the sauce simmer for 5-7 minutes until it thickens.

Add Sour Cream and Mustard: Reduce the heat to low. Stir in the sour cream and Dijon mustard until the sauce is smooth and creamy.

Combine with Beef: Return the cooked beef strips to the skillet. Stir to coat the beef with the sauce. Let it simmer for another 5 minutes to blend the flavors.

Serve: Serve the Beef Stroganoff over cooked egg noodles or rice. Garnish with chopped fresh parsley.