Heat a large skillet over medium-high heat. Add a splash of oil and add beef strips seasoned with salt and pepper. Sear for 2-3 minutes on each side until browned. Remove beef and set aside.

In the same skillet, reduce heat to medium. Add oil if needed, then add finely chopped onions and minced garlic. Sauté for 3-4 minutes until onions are translucent.

Add sliced mushrooms and cook for an additional 5-6 minutes, stirring occasionally until softened and golden.

Lower the heat and stir in Dijon mustard and Worcestershire sauce. Add sour cream and mix until smooth. Cook for another 2 minutes.

Return seared beef to the skillet and stir gently to coat in the sauce. Simmer for 2-3 minutes until warmed through.

Serve over cooked egg noodles, rice, or potatoes. Garnish with fresh herbs if desired.