Heat the oil in a pan. Add the onion and fry until soft, remove from the pan and set aside.
Turn up the heat and quickly brown the beef strips. Add the mushrooms and cook until their juices start to run then add the onions back again.
Add the white wine and let it bubble to reduce a bit. Stir in the Philly and the Dijon mustard until smooth. Serve with rice and fresh vegetables.
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