Optional: Trim and Portion the Flat Iron

1. Skip this step if your steak is already trimmed and portioned.
2. If using a whole flat iron, pat it dry and trim any excess exterior fat.
3. Cut into 2 or 3 steaks, about 1 inch (2.5 cm) thick and 12 oz (340 g) each.

Dry-Brine the Flat Iron Steak

1. If you haven’t already, pat the steak dry on all sides with paper towels.
2. Season both sides with salt equal to about 1% of the steak’s weight. For a 12 oz (340 g) flat iron steak, use about 0.12 oz (3.4 g) of salt, or roughly:
   1 1/4 teaspoons Diamond Crystal kosher salt,
   3/4 teaspoon Morton kosher salt,
   1/2 teaspoon table salt.
3. Place the salted steak on a wire rack over a baking sheet and refrigerate, uncovered, for at least 1 hour, preferably 3 to 4 hours.
4. If you don’t have at least an hour, don’t salt it in advance. Season it immediately before searing, or salt the sliced steak after cooking.

Make the Garlic-Herb Compound Butter

1. Cut the butter into small cubes, place them in a small bowl, and let them sit at room temperature until soft enough to mash with a fork. To speed it up, microwave in 5-second bursts, checking each time to make sure it doesn’t melt completely.
2. Add the garlic, salt, pepper, parsley, and rosemary to the bowl. Mash everything together with a fork, taste and adjust the seasoning, then cover and refrigerate until ready to use.

Preheat the Pan

1. Take the steak and compound butter out of the refrigerator about 15 minutes before cooking.
2. Turn on the exhaust fan or open a window. Heat a heavy skillet over medium-high heat for 3 to 4 minutes, add 2 tablespoons high-smoke-point oil, and heat for 1 more minute. The oil should be shimmering and just starting to smoke.

Pan-Sear the Flat Iron Steak

1. Pat the steak very dry with paper towels, carefully place it in the hot pan, and press it down gently with tongs so it makes good contact with the pan.
2. Cook the steak, flipping every 30 seconds, until it reaches the pull temperature for your desired doneness:
   110°F (43°C) for rare,
   120°F (49°C) for medium-rare,
   130°F (54°C) for medium,
   140°F (60°C) for medium-well,
   150°F (66°C) for well-done.
   See the complete steak temperature chart below.
3. Start checking the internal temperature after about 3 minutes. Insert a meat thermometer horizontally into the thickest part of the steak.
4. Once the steak reaches your target pull temperature, transfer it to a cutting board or plate, top with 1-2 tablespoons of compound butter, and let it rest for 5 minutes.

Slice and Serve

1. Slice the rested steak thinly against the grain and serve with your favorite sides.

Temperature Chart