Add the mushrooms and onion to the frying pan. Season with 1/2 teas salt and cook 6 to 8 minutes, until veggies begin to brown.
Add the flour and tomato paste. Stir and cook for 1 minutes.
Whisk in the beef stock and 1/3 cup wine, scraping the bottom of the pan to remove any browned bits. Add the mustard paste and bring mixture to a simmer.
Lower heat to medium and cook until sauce thickens, 4 to 6 minutes.
Cut the steak into bite sized pieces across the grain. Return the steak and any juices to the bowl. Stir to coat.
Remove the pan from heat and stir in the cream cheese, remaining wine, and chives.
Season with salt and pepper to taste and server over egg noodles or rice.