Cook the egg noodles in salted water until just barely done. Drain and toss with butter to prevent sticking.

Slice the beef thin against the grain.

In a large skillet, sear the beef over medium-high heat until browned, then remove from the pan.

In the same skillet, cook the onions until soft, then add the mushrooms and cook until they release their liquid.

Add minced garlic and cook for an additional 30 seconds.

Stir in the beef broth and Worcestershire sauce (if using).

Mix cornstarch with a little cold water to make a slurry and add it to the sauce to thicken.

Lower the heat, and gradually stir in the sour cream, tempering it to keep it smooth.

Return the beef to the skillet and cook until heated through.

Serve the sauce over the noodles or mix them directly into the sauce.