Cowboy Butter Portobello Sirloin Tips: Easy Crockpot Dinner Step-by-step instructions

Before you start

Before you start, make sure you have a 6-quart slow cooker clean and ready. Trim any excess fat from the sirloin tips and cut them into uniform 2-inch pieces if they're larger. Slice the portobello mushrooms thickly—about 1/2-inch thick—so they hold their shape during the long cook.

Peel the shallots and halve them lengthwise. Cut the cowboy butter into small cubes so it melts evenly. Measure the au jus mix. Have your serving plates and mashed potatoes ready for when the cooking is done.

Instructions

Layer and Season

1. 1Layer the Ingredients
   Place the sirloin steak tips in the bottom of a 6-quart slow cooker in an even layer. Scatter the sliced portobello mushrooms and the peeled shallots over the beef. No need to stir—just let the layers stay as they are.
   Look for The beef should be mostly covered by the mushrooms and shallots.
   Tip Cut any very large steak tips into 2-inch pieces so they cook evenly.
2. 2Add the Butter and Au Jus
   Dot the garlic-herb cowboy butter over the top of the beef and vegetables. Sprinkle the dry au jus mix evenly over everything. Do not add any liquid—the butter and the meat's juices will create the gravy as they cook.
   Look for The butter pieces and au jus powder should cover the top surface.
   Tip If the butter is very cold, let it sit at room temperature for a few minutes so it's easier to dot.

At the end of this phase, you should see the raw sirloin tips at the bottom of the slow cooker, topped with a layer of portobello slices and halved shallots. The butter cubes and au jus powder are scattered over the top, creating a speckled, buttery surface. The raw meat is still red and the mushrooms are firm. Everything is dry and neatly layered, ready to cook.

Slow-Cook to Tender

3. 3Cook Low and Slow
   Cover the slow cooker and cook on LOW for 6 to 7 hours, or on HIGH for 3 to 4 hours, until the beef is fork-tender and the mushrooms are soft. Resist the urge to lift the lid during cooking—every peek lets out heat and adds time. Let it rest for 3 minutes before slicing.
   Look for The meat shreds easily with a fork and the gravy is bubbling gently at the edges.
   Safe temperature 145°F (63°C) internal temperature (steaks, chops and roasts)
   Tip For the most tender results, always choose LOW if time allows.
4. 4Check for Doneness
   After the minimum cooking time, check the beef. It should be fork-tender—a fork should slide in with almost no resistance. If it's still chewy, continue cooking for another 30 minutes and check again. The internal temperature should read at least 145°F (63°C) on an instant-read thermometer. Let it rest for 3 minutes before slicing.
   Look for The meat is tender and the gravy has thickened slightly from the au jus.
   Safe temperature 145°F (63°C) internal temperature (steaks, chops and roasts)
   Tip Because the beef is cooked low and slow, it will be far more tender than a quick seared steak.

After 6 to 7 hours on low, the slow cooker is filled with a bubbling, fragrant gravy. The beef is deep brown and fork-tender, the mushrooms have softened and darkened, and the shallots are translucent and glistening.

The aroma is rich with garlic, herbs, and savory beef. The gravy is thin but glossy, and it coats the back of a spoon. Check the beef for tenderness—it should shred easily.

Rest and Serve

5. 5Rest the Meat
   Turn off the slow cooker and let the beef rest in the hot gravy for at least 3 minutes before serving. This allows the juices to redistribute through the meat, making each bite more succulent.
   Look for The bubbling subsides and the gravy settles.
   Safe temperature 145°F (63°C) internal temperature (steaks, chops and roasts)
   Tip Resting is essential for whole-cut meats, even in a slow cooker.
6. 6Serve Over Mashed Potatoes
   Spoon a generous portion of creamy whipped mashed potatoes onto each plate. Ladle the sirloin tips, mushrooms, shallots, and plenty of the garlic-butter au jus over the potatoes. Serve hot.
   Look for The gravy coats the back of a spoon and the beef is glistening.
   Tip The mashed potatoes soak up the savory butter sauce beautifully.

After turning off the heat and letting the meat rest, the gravy settles and thickens slightly. The beef is moist and tender, the mushrooms are silky, and the shallots are sweet. The garlic-butter au jus pools around the meat, ready to be spooned over mashed potatoes. The dish looks rustic and inviting, with steam rising and a golden sheen from the butter. Serve immediately.

Common mistakes

The most common mistake is peeking too often. Every time you lift the lid, heat escapes and adds 15 to 20 minutes of cooking time. Trust the recipe and keep the lid on. Another mistake is using a lean cut like tenderloin, which can dry out in the slow cooker.

Stick with sirloin tips or chuck. Don't skip the rest time after cooking—it lets the juices redistribute. Finally, don't add extra liquid; the butter and meat juices are enough to create a flavorful sauce.

How to tell it’s done

The dish is done when the beef is fork-tender, meaning a fork slides into the meat with almost no resistance and it separates easily. The internal temperature should read at least 145°F (63°C) on an instant-read thermometer, but because it cooks low and slow, it will likely be well above that and still juicy.

The mushrooms should be soft and silky, and the shallots should be translucent and sweet. The gravy will be thin but flavorful; if you want it thicker, remove the meat and veggies, then simmer the liquid with a cornstarch slurry on the stovetop for a few minutes.

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