°600 g / 1.2 lb Scotch fillet steak / boneless rib (note 1)
°2 tablespoons vegetable oil, divided
°1 onion (or 2 small onions)
°300g/10oz mushrooms, sliced ​​(not too thin)
°40 g/3 tablespoons butter
°2 tablespoons flour (note 2)
°2 cups/500ml beef broth, preferably with less salt
°1 tablespoon Dijon mustard
°150 ml / 2/3 cup sour cream
°Salt and Pepper


Use your fist (or a rolling pin or mallet) to flatten the steaks 3/4 cm/1/3 thick. Cut into 5mm/1/5th strips (cut the long strips in 
half), shake off the excess fat.
Sprinkle a little salt and pepper.
Heat 1 tsp of oil in a skillet on high heat. Spread half of the meat in the skillet, spreading it out with quick tongs. Leave it untouched for 30 seconds until it turns brown. Turn the beef quickly (as best you can!). Immediately remove it on the plate. Don't worry about the pink bits and they will be raw on the inside.
Add the remaining 1 tablespoon oil and repeat with the remaining beef.

Reduce the heat to medium-high. Add butter and melt. Then add the onions and cook for 1 minute, then add the mushrooms.
Cook mushrooms until golden. Scrape the bottom of the pan to remove all the gold (that's flavor!).
Add flour and cook, stirring, for 1 minute.
Add half of the broth while stirring. Once combined, add the remaining broth.
Stirring, then adding sour cream & mustard. Stir until combined (don't worry if it looks split, the sour cream will "melt" as it heats up).

Bring the mixture to a simmer, then reduce the heat to medium-low. Once it has thickened to the consistency of a pouring cream (3 - 5 minutes), adjust salt and pepper to taste.
Add the beef again (including the juices). Simmer about 1 min, & removing  from stove directly.

Enjoy !