01 -
Flatten the steak with a mallet until it's about 0.75cm thick, then slice it into narrow pieces, roughly 0.5cm wide. Add salt and pepper to coat the pieces well.
02 -
Heat up some oil in your skillet until it's hot. Cook the meat in two separate turns, letting it sizzle in one layer at a time. Flip after about 30 seconds per side – you want it browned but still juicy inside. Take it out onto a plate.
03 -
Drop the heat to medium and melt the butter in the same pan. Stir in the sliced onions for a minute, then add mushrooms. Let them cook together until golden brown, stirring occasionally and scraping up all flavorful bits stuck to the pan.
04 -
Sprinkle the cooked mushrooms and onions with flour, then mix it in. Slowly pour the beef broth while stirring to keep it smooth. Add sour cream and Dijon mustard, continuously mixing. Let the sauce bubble gently for 3–5 minutes until it thickens.
05 -
Toss the cooked beef (along with resting juices) back into the pan. Warm it up for about a minute, then remove from heat. Serve over hot noodles or pasta, topping with chives if you feel like adding them.