Pan-Seared Flat Iron Steak with Mushroom Pan Sauce
Pan-seared flat iron steak with mushroom pan sauce is my answer to a steakhouse craving on a weeknight. Flat iron is one of the most underrated cuts at the butcher counter — tender, beefy, evenly cut, and so much cheaper than a ribeye. Sear it hard, baste it in butter, then use the same skillet to build a glossy red wine and mushroom sauce while the steak rests. Dinner for two, one pan, under an hour.
Servings: 2 servings
Calories: 581kcal
Equipment
Ingredients
For the Steak
- 8-12 oz (227-340g) flat iron steak
- Kosher salt
- Freshly ground black pepper
- 2 Tbsp (30ml) neutral oil
- 2 Tbsp (28g) unsalted butter
- Fresh chives, thinly sliced
- Flaky sea salt
For the Mushroom Sauce
- 8 oz (227g) whole baby bella mushrooms, stems removed, caps cleaned and very thinly sliced
- 1 large shallot, finely diced
- Kosher salt
- ½ cup (120ml) red wine — something good enough to drink
- 1 Tbsp (15g) beef or veal demi-glace (note: if needed, verify this is gluten-free)
- 1 tsp (5g) Dijon mustard
Instructions
- Season the steak. Bring the steak to room temperature about 20 minutes prior to cooking. Season generously on both sides with kosher salt and black pepper.
- Sear the steak. Heat a large cast-iron or stainless steel skillet over medium-high heat. Add 2 Tbsp (30ml) neutral oil. When just beginning to smoke, add the steak and cook undisturbed for 4 minutes, or until a deep crust forms. Carefully flip the steak(s), add 2 Tbsp (28g) of unsalted butter, then cook for another 3-4 minutes for medium-rare while basting with a spoon. Transfer to a plate, then rest for 10 minutes. Reduce the heat to medium.
- Make the sauce. To the pan, add (227g) sliced mushrooms, then cook, stirring occasionally, until they turn golden brown, about 4-6 minutes. Add diced shallot and ½ tsp kosher salt, stir, then cook for about 1-2 minutes more. Deglaze with ½ cup (120ml) red wine. Use a spatula to scrape up any bits from the bottom of the pan. Bring to a boil, cook for a minute, then stir in 1 Tbsp (15g) demi-glace and 1 tsp (5g) Dijon mustard. Allow this to simmer and reduce for 1-2 minutes, then taste and adjust seasoning. Remove from the heat.
- Serve! Slice the steaks against the grain, then transfer to individual plates or a large platter. Spoon the mushroom pan sauce all around the steak, then finish by sprinkling with thinly sliced chives and flaky sea salt. Enjoy!
Tip: If you have kitchen weights or a press, you can place one or two of them on top of the steak as it sears on the first side. This helps it to brown evenly.
Internal temperature guide: Note that the temperature will continue to rise as the steak rests, so I recommend removing it before the desired doneness is reached. Once rested, the final temperature should read: 125°F (52°C) for rare, 130°F (54°C) for medium-rare, or 135°F (57°C) for medium.
Notes
- Nutrition facts calculated with a 10oz steak and exclude garnishes.
- Make-ahead: the mushroom sauce can be made 2 days ahead and gently rewarmed with a splash of stock or water. The steak is best cooked and served fresh. Store leftover steak and sauce separately.
- Freezing: The sauce freezes well for up to 2 months. I don't recommend freezing cooked steak.
- Steak swaps: Hanger, sirloin, or NY strip; adjust timing for thickness and use a thermometer.
Nutrition
Calories: 581kcal | Carbohydrates: 11g | Protein: 32g | Fat: 41g | Saturated Fat: 14g | Polyunsaturated Fat: 11g | Monounsaturated Fat: 11g | Trans Fat: 1g | Cholesterol: 124mg | Sodium: 3201mg | Potassium: 1080mg | Fiber: 1g | Sugar: 4g | Vitamin A: 356IU | Vitamin C: 1mg | Calcium: 47mg | Iron: 5mg
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