Prep the beef. Pat the beef dry and slice it thinly against the grain. Season with salt and pepper. Dry beef sears better and stays tender.

Sear in batches. Heat a large skillet over medium-high. Add olive oil and half the butter. Sear the beef in a single layer, 1–2 minutes per side, just until browned. Remove to a plate and repeat with remaining beef. Do not overcook.

Cook the mushrooms and onions. Lower heat to medium. Add the remaining butter, then the mushrooms. Let them brown undisturbed for a couple of minutes, then stir. Add the onion and a pinch of salt. Cook until softened and lightly caramelized, 6–8 minutes.

Add garlic and seasoning. Stir in the garlic, smoked paprika, and a few grinds of pepper. Cook 30 seconds until fragrant.

Deglaze with broth. Pour in the beef broth and Worcestershire sauce. Scrape up the browned bits from the pan. Simmer for 2–3 minutes to reduce slightly.

Make it creamy. Stir in the heavy cream and Dijon mustard. Simmer gently for 3–4 minutes until the sauce thickens enough to coat a spoon. Keep the heat medium-low to avoid curdling.

Finish with sour cream. Remove the pan from heat. Whisk in the sour cream until smooth. Taste and adjust salt, pepper, or Worcestershire. If you like a little brightness, add a tiny squeeze of lemon.

Return the beef. Add the seared beef (and any juices) back to the skillet. Toss to coat and warm through for 1–2 minutes. Avoid boiling once sour cream is in.

Garnish and serve. Sprinkle with chopped parsley. Serve over zucchini noodles, riced cauliflower, spaghetti squash, or with sautéed cabbage for a hearty low carb plate.