Creamy Mushroom Sauce on Grilled Flat Iron Steak

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Flat iron steaks are one of the most underappreciated types of beef available today.

When grilled properly, you’ll get a juicy, tender steak that’s full of flavor.

In this recipe, I’ll teach you how to make my favorite grilled flat iron steak. The creamy mushroom sauce will improve on an already delicious dish.

What is a Flat Iron steak?

Grilled Flat Iron Steak With Creamy Mushroom Sauce

Have you ever tried a Flat Iron steak?

It isn’t the most popular steak cut and is sometimes overshadowed by the more famous Filet Mignon, but don’t let that mislead you. When it comes to softness, the Flat Iron steak rivals even the best grade Filet Mignon.

The Flat Iron (often abbreviated to flatiron) steak is made from primal chuck, which is cut from the shoulder and delivers beef with a deep meaty taste, softness, and excellent marbling. Other names for this cut of meat are Oyster Blade Steak, Butler Steak, and Top Chuck Steak.

The flat iron has a consistent thickness and a rectangular shape. It benefits from being cooked to a nice medium rare because of its muscular composition. Anything more than medium (145F) and the steak will begin to dry out rapidly.

Reverse searing: Worth the hype?

Grilled Flat Iron Steak With Creamy Mushroom Sauce

Searing is a classic cooking method that begins with a sear over direct fire and then finishes the piece of meat over indirect heat.

Reverse searing has recently acquired appeal in the culinary world. A reverse sear allows you to get a tasty crust on your steak while maintaining a more uniformly cooked internal temperature throughout the remainder of the meat.

Because it is seared at a high temperature initially and then continues to cook over indirect heat after the sear, a classic sear tends to leave a ring of well-done flesh around the exterior of the steak.

Both ways provide an excellent flatiron steak, but the reverse sear approach yields superior texture and a more uniform cook on the inside of the steak.

For any portions of beef thicker than 1.5 inches, I like to reverse sear.

How to grill flatiron steak

1. Season with a simple SPG rub

Some people want to get creative with their steak spice mixes and marinades, but I feel that when dealing with excellent meat, simplicity is crucial.

I took the Flat Iron out of the refrigerator and let it rest for 1 hour to get it up to room temperature for this preparation.

The Kosmos Q SPG Rub was used to season the flat iron steak. It’s a unique combination of sea salt, black pepper, and garlic, with a dash of sugar and spices to enhance the taste of steak, chicken, and pig.

2. Fire up the grill for two-zone cooking

Nothing beats a nice steak grilled over charcoal, so we utilized the flexible Nomad Grill and configured it for two-zone grilling.

Two-zone cooking is a technique in which one side of the grill produces high-temperature, direct heat while the other side produces no heat, allowing the meat to cook indirectly.

We just moved the coals to one side of the grill and let the steak roast on the other.

If you’re using a gas grill with many burners, you may achieve the same effect by turning off one of them.

We smoked it at around 250 degrees Fahrenheit on the indirect side until the steak reached an internal temperature of 110 degrees Fahrenheit.

At that time, we switched the steak to the direct heat side, directly over the charcoal, and reverse-sear it until it reached 130F internal temperature.

3. Patience is a virtue: It’s time to rest

The resting time after cooking is perhaps one of the most crucial procedures in making a great steak. If you bite into your steak right after it comes off the grill, you will lose a lot of the taste that you worked so hard to obtain.

As beef cooks, the muscle fibers flex, pushing the water in the steak to the exterior. The resting interval enables the flesh to cool gradually, and as the temperature drops, the constricted muscle fibers begin to relax.

Furthermore, the tightened muscle fibers will reduce pressure in the middle of the steak, and the moisture in the flesh will redistribute evenly, sealing in all of the juice and taste that makes a good steak fantastic.

The resting time varies depending on the size of the steak, but we let our Flat Iron rest for around 10 minutes.

We prefer to tent steaks with foil to retain as much heat as possible, resulting in a perfectly cooked, juicy steak that is bursting with flavor.

Making the creamy mushroom sauce

While your steak rests, prepare the creamy mushroom sauce. You may serve this steak on its own, but the mushroom sauce complements it well.

Place a cast-iron pan over hot grill embers and sprinkle with olive oil. Place the cut onions in the pan and season with salt. Allow the onions to simmer for approximately 3 minutes, or until transparent.

Then, in the same pan, sauté the mushrooms until soft, approximately 5 minutes.

Once the mushrooms and onions are soft and tender, add the heavy cream, Dijon mustard, Worcestershire sauce, grated parmesan, and cracked black pepper to taste.

Give the sauce a good stir and simmer for another 5 minutes.

The beautiful thing about the sauce is that it is really customizable; you can add more of anything you want and truly customize it! It’s also delicious when served with asparagus or broccoli.

Serving your flat iron steak

When your steak has rested and your sauce is ready, slice it and place it on a platter. Place the mushroom cream sauce on top of the steak and serve.

Other steak recipes to try

  • Steak Cooked Directly on the Coals Caveman Style
  • Porterhouse Steak Grilled with Whisky Compound Butter
  • Authentic Grilled Carne Asada
  • Tomahawk Steak Reverse Seared with Garlic Butter Mushrooms and Grilled Asparagus

Sides for grilled steak

  • Homemade Classic French Fries
  • Smoky Garlic Butter Mushrooms
  • Celery and Parmesan Salad
  • Ultra Crispy Triple Cooked Potato Wedges

Grilled Flat Iron Steak Recipe


What is the best way to cook flat iron steak?

If preferred, season the steaks with salt, pepper, and steak spice. Sear the steaks in the skillet for 2-3 minutes on each side. If further cooking time is required to get the desired degree of doneness, reduce the heat to low and cook for another 2-5 minutes. Rest for 5 minutes on a platter covered with foil.

How to cook a flat iron steak on the grill?

Grill a 12-inch steak for 12-14 minutes, flipping once before the halfway mark. A meat thermometer should read 130 degrees Fahrenheit. Rest your steaks for 5 minutes before serving, loosely covered with foil.

What is mushroom steak sauce made of?

This sauce begins with a large amount of fresh sliced mushrooms sautéed in butter till golden brown. Garlic is used to flavor the dish, while flour is utilized as a thickening factor. Add beef stock, Worcestershire sauce, and pan drippings from your cooked steak next.

What is mushroom cream sauce made of?

However, they need some taste enhancement. This is where this clever sauce comes in: It’s made with three simple ingredients (heavy cream, garlic, and mushrooms), cooks in one pan, and can be whipped up in under 30 minutes.

How do you make Jamie Oliver creamy mushroom sauce?

In a big heated skillet, melt the butter and add a drizzle of olive oil, the mushrooms, sliced onion, and a generous dose of salt and pepper. Stir everything around and cook for about 8 minutes, or until the onions have softened and the mushrooms are starting to caramelize and take on colour.

How long does it take to grill a flat iron steak?

Grill your flat iron steaks hard on one side, a good 5 minutes without touching them. Flip and grill to the doneness you like, anywhere from 2 to 10 minutes, depending on the heat and the thickness of your steak.

How long should I sear a flat iron steak?

How do you cook a flat iron steak on the stovetop? Sear the steaks for 2-3 minutes each side for medium-rare, or 4 minutes per side for well-done. Turn the heat to low, and continue cooking for another 3-8 minutes until your preferred temperature is reached.

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