Guinness Flat Iron Steak

Guinness Flat Iron Steak Recipe

For this recipe I put an Irish spin on a flat iron steak for St. Patrick’s Day. Flat Iron steak is my go to cut for a quick and inexpensive dinner. Pair them with this killer mushroom sauce and some roasted potatoes, and you have a great dinner for any night!

Guinness Flat Iron Steak Ingredients 

Guinness Flat Iron Steak Marinade

Combine ingredients in a small bowl and use as a marinade for beef.

Guinness Mushroom Sauce


  • 2 Tablespoons salted butter
  • 1 small shallot finely chopped
  • 4-5 cloves garlic minced
  • 8oz sliced baby Bella mushrooms
  • 1/2 teaspoon Kosher Salt
  • 1/2 teaspoon Black Pepper
  • 1/4 cup Worcestershire sauce
  • 1/4 cup soy sauce
  • 1 Tablespoon balsamic vinegar
  • 1 cup Guinness stout beer
  • 1 teaspoon corn starch
  • 1 teaspoon cold water

Melt butter in a sauce pan over medium heat. Add shallot and garlic and sauté for 2 minutes. Add sliced mushrooms and season with AP seasoning. Sauté for 2-3 minutes until mushrooms are tender. Add Worcestershire, soy, and balsamic reduce for 3-4 minutes; add Guinness and reduce volume by half (approx 5-7 minutes). Combine corn starch and cold water in a small bowl and whisk into sauce. Allow the mixture to reach a slight boil and remove from heat. Serve warm over steak.

Smoked Potatoes

  • 1lb baby Yukon gold potatoes
  • 1 Tablespoon Olive Oil
  • 1/2 Tablespoon Kosher Salt
  • 3 Tablespoon melted butter
  • 1/2 teaspoon dried parsley
  • 1/4 teaspoon Killer Hogs AP Seasoning

Rinse and dry potatoes, place potatoes on foil lined baking sheet, drizzle with olive oil and season with Kosher Salt. Prepare pellet smoker or other grill for indirect cooking at 400 degrees. Place the baking sheet on the grill and cook for 30 minutes or until potatoes are tender. Use a skewer to check potatoes. It should slide in with little resistance. Melt butter in a small bowl, add parsley and AP seasoning. Drizzle over warm potatoes and serve. 

Guinness Flat Iron Steak Directions 

  1. Remove flat iron steak from packaging and trim excess silver skin; place the flat iron in a 1 gallon size zip top bag. Combine the ingredients for the marinade in a small bowl and pour over steak. Marinate for 1 hour.
  2. Prepare charcoal grill for direct grilling at 500 degrees. While grill is heating prepare Guinness Mushroom sauce as directed above.
  3. Remove the flat iron steak from the marinade allowing excess moisture to drip back into zip top bag. Season the steak with Killer Hogs Steak Rub on all sides.
  4. Place the steak on the grill and cook for 5 minutes. rotate the steak after 2.5 minutes to create grill marks. Repeat the same step for the opposite side for a total cook time of 10 minutes or until the steak reaches 125 internal temperature - medium rare.
  5. Rest the flat iron for 5-7 minutes before slicing and serve topped with Guinness Mushroom sauce. 

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