Over medium-high heat, melt 2 tablespoons of butter. Sauté the steak slices in a single layer for about 2-3 minutes on each side. Season with kosher salt and pepper. When seared, transfer steak to a plate and set aside. 

Melt the remaining 2 tablespoons of butter in the sauté pan. Add the onions and sauté for about 5 minutes. Add mushrooms and sauté, stirring occasionally, until the mushrooms are cooked and the onions are soft. 

Add the garlic and sauté for 1 minute, stirring occasionally.  Then add the white wine and deglaze the pan by using your cooking spoon to scrape the brown bits off the bottom of the pan. Let the mixture cook down for an additional 3 minutes.

While the wine cooks down, whisk together the beef stock, Worcestershire sauce and flour until smooth in a separate bowl. 

Pour the beef stock mixture into the sauté pan, stir to combine, then let the mixture simmer for 3 minutes, stirring occasionally. Add the seared beef back to the pan and stir to combine. If the sauce is too thick, you can add more beef broth to reach a looser consistency. 

Cut the heat and stir in the sour cream, dijon mustard until combined. Taste and season with additional salt and pepper if needed.

Portion noodles into bowls, top with beef mixture, then top each serving with breadcrumbs or croutons, sprinkle with chopped parsley.