Cowboy Butter Mushroom Flank Steak Crockpot Dinner Step-by-step instructions

Before you start

Before starting, slice the flank steak against the grain into thin strips, about 1/4-inch thick. This helps the meat become tender during the long cook. Dice the onion and slice the mushrooms if not using pre-sliced.

Have the condensed soup, cowboy butter, and au jus mix ready. No need to preheat the slow cooker; just place the ingredients in the cold insert and turn it on. For easy cleanup, consider using a slow cooker liner.

Instructions

Layer and Season

1. 1Layer the Beef and Aromatics
   Place the sliced flank steak strips in the bottom of a 6- to 7-quart slow cooker. Spread the diced onion over the beef. Pour the condensed cream of mushroom soup over the top, using a spatula to spread it evenly. Add the sliced mushrooms if using.
   Look for The beef is covered with a creamy layer and onions are scattered throughout.
   Tip For best texture, slice the steak against the grain into thin strips, about 1/4-inch thick.
2. 2Add the Butter and Au Jus
   Dot the garlic-herb cowboy butter over the top of the soup mixture. Sprinkle the dry au jus mix evenly over everything. Do not stir.
   Look for The butter pats sit on the surface, and the au jus powder forms a light coating.
   Tip Leaving the butter on top allows it to melt slowly and infuse the sauce as it cooks.

You'll see the raw beef, onions, and soup in distinct layers, with the butter and au jus mix on top. The colors should be vibrant, and the butter will start to soften as the slow cooker warms. This is a good time to ensure all ingredients are evenly spread, but avoid stirring.

Slow-Cook and Rest

3. 3Slow-Cook Until Tender
   Cover the slow cooker and cook on LOW for 6 to 8 hours, or on HIGH for 3 to 4 hours, until the beef is fork-tender and easily shreds. Avoid opening the lid during cooking to keep the heat steady. Let it rest for 3 minutes before slicing.
   Look for The sauce is bubbling gently, and the beef is tender enough to pull apart with a fork.
   Safe temperature 145°F (63°C) internal temperature (steaks, chops and roasts)
   Tip If the sauce seems thin at the end, remove the beef and simmer the sauce on HIGH uncovered for 15 minutes to thicken.
4. 4Rest the Beef
   Turn off the slow cooker and let the beef rest in the sauce for at least 5 minutes. This allows the juices to redistribute, keeping the meat moist.
   Look for The beef rests in the rich gravy, absorbing flavor.
   Tip Resting is essential for tender, juicy slices.

After 6 to 8 hours on LOW, the kitchen will smell richly savory. The sauce will be bubbling, the beef will be visibly tender, and the mushrooms will have softened.

The butter and soup will have melded into a golden gravy. The beef should easily shred with a fork. Let it rest for at least 5 minutes before serving to lock in the juices.

Serve and Savor

5. 5Serve Over Mashed Potatoes
   Spoon the beef, mushrooms, and gravy over a bed of whipped mashed potatoes on each plate. Serve hot, with extra gravy spooned over the top.
   Look for Steaming beef and gravy coat the creamy potatoes.
   Tip For a low-carb option, serve over cauliflower mash or steamed rice.

When you spoon the beef and gravy over the mashed potatoes, the steam will rise and the sauce will coat the meat in a glossy, appetizing sheen. The potatoes will be creamy and the beef tender. Serve immediately, and watch it disappear.

Common mistakes

One common mistake is opening the slow cooker lid too often, which releases heat and extends cooking time. Trust the process and keep the lid on. Another is using a lean cut without enough fat—flank steak is ideal, but if you use a very lean cut, it can dry out.

Also, don't skip the rest time; cutting into the beef too soon can cause juices to run out, making the meat dry. Finally, resist the urge to stir the ingredients before cooking—layering them as directed ensures the best texture and flavor distribution.

How to tell it’s done

The beef is done when it is fork-tender and easily pulls apart with minimal resistance. The sauce should be bubbling gently and have thickened slightly.

If you have a meat thermometer, the internal temperature of the beef should read at least 145°F (63°C) for medium-rare, but for slow-cooked flank steak, it will likely be higher, which is fine. Let the beef rest for at least 5 minutes before serving to allow the juices to redistribute.

• Steaks, chops and roasts: 145°F (63°C) in the thickest part, then a 3-minute rest