1. Heat olive oil in a large skillet over medium-high heat. Add beef sirloin and cook until browned on both sides. Remove from skillet and set aside.
2. In the same skillet, melt butter over medium heat. Add onion and garlic and cook until softened.
3. Add sliced mushrooms to the skillet and cook until they release their moisture and start to brown.
4. Pour in beef broth and bring to a simmer. Cook for 5 minutes, stirring occasionally.
5. Stir in sour cream and Dijon mustard until well combined.
6. Add the cooked beef back into the skillet and stir to combine with the sauce.
7. Season with salt and pepper to taste. Serve hot, garnished with fresh parsley.
Enjoy your delicious Keto Beef Stroganoff with Mushroom!