01 -
Flatten steaks to 3/4cm thick, slice into 5mm strips.
02 -
Season meat with salt and pepper.
03 -
Heat half the oil in large skillet on high heat. Quick sear half the beef for 30 seconds each side, remove to plate. Repeat with remaining oil and beef.
04 -
Lower heat to medium-high, add butter and melt. Cook onions 1 minute, then add mushrooms until golden.
05 -
Add flour, cook 1 minute, stirring. Gradually stir in beef broth.
06 -
Add sour cream and mustard, stir well. Simmer until sauce thickens like cream (3-5 minutes).
07 -
Return beef and plate juices, simmer 1 minute only.