Thinly slice the beef against the grain into strips about 1/4 inch thick. Lightly season with salt and pepper and set aside.

Heat a tablespoon of butter or oil in a large skillet over medium-high heat. Sear the beef strips in batches for 2-3 minutes until browned. Remove and set aside.

In the same skillet, add another tablespoon of butter or oil. Sauté chopped onions for 4-5 minutes until soft. Add mushrooms and cook for 5-7 minutes until golden brown.

Add minced garlic and stir for 30 seconds. Optionally sprinkle in paprika and stir to combine.

Pour in beef broth, scraping the bottom to deglaze. Simmer for 3-4 minutes.

Mix 1 tablespoon of flour with water to create a slurry, then stir into the simmering broth. Cook for 2-3 minutes until sauce thickens.

Return the beef to the skillet, stirring to coat. Cook for another 2-3 minutes until heated through.

Off the heat, stir in sour cream until smooth and creamy.

Serve immediately over egg noodles, rice, or mashed potatoes, garnished with parsley if desired.