Cook the beef: In a large skillet, heat the butter and olive oil over medium-high heat. Season the beef with salt and pepper, then sear the beef strips for 2-3 minutes per side until browned. Remove the beef from the skillet and set aside.

Sauté the onions, garlic, and mushrooms: In the same skillet, add the chopped onions and garlic. Sauté for 3-4 minutes until softened. Add the mushrooms and cook for another 4-5 minutes until they release their moisture and begin to brown.

Make the stroganoff sauce: Stir in the beef broth, heavy cream, Dijon mustard, and Worcestershire sauce (if using). Let the sauce simmer for 5-7 minutes, allowing it to thicken slightly. Stir in the sour cream and adjust seasoning with salt and pepper to taste.

Add the beef back: Return the seared beef to the skillet, tossing it in the creamy mushroom sauce. Let it simmer for 3-4 minutes until the beef is warmed through.

Prepare the zoodles: While the beef is simmering, quickly sauté the spiralized zucchini noodles (zoodles) in a separate pan over medium heat for 2-3 minutes until just tender, or serve them raw for a crunchier texture.

Serve: Plate the beef stroganoff over the zoodles and garnish with fresh parsley. Serve hot and enjoy this keto-friendly twist on a classic comfort dish!