- Melt butter in large skillet over medium heat. Add mushrooms and onions and cook, stirring occasionally, until tender and light golden brown, about 10 minutes.
- Stir in flour and cook, until smooth, about 1 minute. Whisk in broth and Worcestershire sauce, and bring to a boil over medium-high heat. Stir in beef and reduce heat to medium-low. Simmer until beef is fully heated through and sauce thickens, about 10 to 15 minutes.
- Stir in sour cream until combined. Serve over egg noodles and top with parsley.
Tip: Pre-sliced onions and mushrooms can usually be found in the produce aisle of your local grocer.