Slice beef into thin strips, about ¼ inch thick. Chop the onion, slice mushrooms, and mince garlic.

Melt 1 tablespoon of butter over medium-high heat in a large skillet. Season beef with salt and pepper, add to skillet, and sear for 1-2 minutes per side until browned.

Add remaining butter to the skillet. First, add chopped onions, then sliced mushrooms. Sauté for 4-5 minutes until softened, then stir in minced garlic and cook another 30 seconds.

Pour in beef broth and deglaze the pan, scraping up browned bits. Stir in Worcestershire sauce and Dijon mustard. Let simmer for 2 minutes.

Reduce heat to low and whisk in cream cheese until melted. Stir in sour cream gently to avoid boiling.

Return seared beef to the skillet, toss in the sauce, and cook for another 1-2 minutes until heated through.

Serve over cauliflower mash or zucchini noodles, garnished with parsley.