Put a pot of water on to boil, for pasta. In a separate pan, heat olive oil over medium heat until shimmering. Cook diced onion, garlic, and ground beef in oil until browned, about 10 minutes. Drain fat.
Add sliced mushrooms to pan and cook 2-3 more minutes. Sprinkle flour over top, stir in, and cook another minute or two.
Add to pan the broth, Worcestershire sauce, salt and pepper; bring to a boil. Reduce heat and simmer on low until liquid has thickened slightly, about 10 minutes. While sauce is reducing, cook egg noodles in the pot according to package directions.
Remove beef mixture from heat, and stir in sour cream and parsley flakes.