Pat the steak dry with a paper towel and cut it into ½-thick strips or 1-inch cubes.

Season the beef with salt and pepper, then toss with 1 tablespoon of flour. Shake off any excess flour.

In a large skillet or saucepan, heat olive oil over medium-high heat. Brown beef in small batches for about 1 minute on each side until lightly browned. Transfer to a plate and set aside.

Reduce the heat to medium. Add butter and onion to the pan, cooking until the onion is softened, about 4-5 minutes. Add the mushrooms and garlic, continuing to cook until softened, about 4 minutes.

Add the remaining 2 tablespoons of flour to the mushroom mixture and cook for one minute.

Add the broth, Worcestershire sauce, mustard, and thyme. Bring to a boil, reduce the heat, and let simmer uncovered for 5 minutes.

Add the browned beef and any juices on the plate to the sauce. Cook for an additional 2 minutes or until the beef is heated through.

Remove from the heat and gently stir in sour cream. Season with salt and pepper to taste. Serve over egg noodles and garnish with parsley.