In a large skillet, heat the olive oil over medium-high heat. Once hot, add the beef slices, seasoning with salt and pepper. Cook for about 2-3 minutes until browned but still juicy. Remove from the skillet and set aside.

In the same skillet, add the chopped onion, cooking until soft and translucent—about 3-4 minutes. Stir in the minced garlic and sliced mushrooms, cooking until the mushrooms are tender.

Pour in the beef broth, scraping any bits stuck to the bottom. Add the heavy cream, Dijon mustard, and Worcestershire sauce. Stir well and let it simmer for about 5-7 minutes until it thickens slightly.

Add the beef back into the skillet, stirring to coat it in the sauce. Taste and adjust seasoning if needed. Serve hot, garnished with fresh parsley.