Slice the beef into thin strips, about 1/4-inch thick. Chop the onion and slice the mushrooms, then mince the garlic. Set everything aside for smooth cooking.

In a large skillet, melt 1 tablespoon of butter over medium-high heat. Once sizzling, add the beef in a single layer, seasoning with salt and pepper. Sear until browned, about 1-2 minutes per side, then transfer to a plate.

Add the remaining tablespoon of butter to the same skillet. Toss in the chopped onion and sliced mushrooms, cooking until the onions are soft and mushrooms are golden brown, about 4-5 minutes. Stir in the minced garlic and cook for another 30 seconds until fragrant.

Pour in 1 cup of beef broth, scraping the browned bits from the bottom of the skillet. Lower the heat to medium, then stir in the Worcestershire sauce and Dijon mustard, letting it simmer gently for 2 minutes.

Whisk in 4 oz of cream cheese until it’s melted and smooth. Then, fold in 1/2 cup of sour cream, stirring until creamy and well combined. Make sure to keep the heat low; do not let it boil!

Return the seared beef and any juices from the plate back into the skillet. Toss everything to coat in that rich sauce, heating through for an additional 1-2 minutes.