1 lb (450 g) beef sirloin or flank steak, thinly sliced against the grain
Salt and freshly ground black pepper
2 tbsp vegetable oil or neutral oil
2 tbsp unsalted butter
1 medium onion, finely sliced
10–12 oz (300–350 g) cremini or button mushrooms, sliced
2 cloves garlic, minced
1 tbsp Dijon mustard
1 cup beef broth (or low-sodium broth)
1/2 cup dry white wine or additional broth
1 cup sour cream, room temperature
1–2 tsp Worcestershire sauce
1–2 tsp cornstarch mixed with 1 tbsp cold water (optional)
Fresh parsley or chives, chopped
Cooked egg noodles, mashed potatoes, or rice for serving
Instructions
Prep the beef: Pat the thin slices dry and season both sides with salt and pepper. Heat a large skillet over medium-high until shimmering.
Sear the beef quickly: Add 1 tbsp oil to the hot pan and in a single layer sear the beef for 45–60 seconds per side until browned but still slightly pink inside. Transfer to a plate—don’t overcook; it will finish in the sauce.
Brown aromatics and mushrooms: Lower heat to medium, add remaining oil and 1 tbsp butter. Toss in the onions and sauté until soft and translucent, about 4 minutes. Add mushrooms and cook until deeply browned and their moisture has evaporated, another 6–8 minutes.
Add garlic and mustard: Stir in garlic and Dijon for 30 seconds until fragrant. Scrape up any brown bits from the bottom of the pan.
Deglaze and simmer: Pour in wine (or extra broth) and let it reduce by half, about 2–3 minutes. Add the beef broth and Worcestershire sauce, bring to a gentle simmer.
Return beef to pan: Slide the seared beef and any juices back into the skillet. Simmer together for 1–2 minutes to meld flavors—beef should be tender and sauce slightly reduced.
Finish with sour cream: Remove pan from direct heat and stir in room-temperature sour cream until smooth. If you prefer a thicker sauce, whisk the cornstarch slurry into the sauce and simmer for 1 minute more. Taste and adjust salt, pepper, and mustard.
Garnish and serve: Sprinkle with chopped parsley or chives and serve over buttered egg noodles, mashed potatoes, or rice. Spoon plenty of sauce over each portion.
Notes
Tender strips of beef in a silky mushroom-and-Dijon sauce that delivers restaurant-style richness with minimal fuss—perfect for busy weeknights or a cozy date night.
