Heat a large sauté pan and add oil and butter. Sauté onions until
translucent but not brown. Set aside. Add more oil and butter if needed;
sauté mushrooms until lightly browned and set aside with onions.
Dredge the meat in the flour seasoned with salt and pepper. Shake off
excess flour and brown the meat in small batches. Don't overcrowd the pan
or the meat will steam and not brown. Set meat aside with onions and
season with salt and pepper.
Deglaze the pan by adding the wine and scraping the bits from the bottom
of the pan, called fond. Reduce slightly and add the mustard,
Worcestershire sauce and stock. Return onions, mushrooms and steak to the
pan and simmer until slightly thickened.
Reduce heat to low and stir in the creme fraiche, re-season with salt and
pepper, heat until warmed through and serve over egg noodles.