Heat oil in a large skillet over high heat. Add beef in a single layer (in batches if needed) and sear 2 minutes per side until browned. Transfer to a plate.

Reduce heat to medium, add more oil if the pan looks dry, then add mushrooms and onion with a pinch of salt. Cook, stirring occasionally, until mushrooms release liquid and onion softens, about 5 minutes.

Pour in beef broth, scraping up browned bits. Bring to a simmer and cook until slightly reduced, 3 to 4 minutes. Season with salt and pepper.

Remove skillet from heat, stir in sour cream until smooth. Return beef and any juices to the skillet, toss to coat. Serve over noodles.