Dinner · Part 3 of 3: Tips & recipe card

Slow-Cooker Cowboy Butter Flank Steak with Peppers Tips, FAQ & printable recipe

Name: Slow-Cooker Cowboy Butter Flank Steak with Peppers
Prep time: 10 min
Cook time: 8 h
Total time: 8 h 10 min
Cuisine: American
Ingredients: 2 lb flank steak, thinly sliced against the grain; 2 bell peppers (1 green, 1 red), sliced into thick strips; 1 red onion, cut into wedges; 2 sticks garlic-herb cowboy butter, cut into pieces; 1 oz dry au jus mix

By Clara Weller · Oct 28, 2026

Slow-cooker cowboy butter flank steak with bell peppers and red onions in a rich au jus, served on a white plate.

Prep: 10 min
Cook: 8 h
Total: 8 h 10 min
Serves: 6

Tips for success

For the best flavor, sear the flank steak in a hot skillet for a minute per side before adding it to the slow cooker.

This adds a deep, caramelized crust that enriches the final dish, but it's optional for a truly dump-and-go meal. If you do sear, do it in batches to avoid overcrowding the pan, and use a little oil to help browning.

To make the dish even more hearty, add sliced mushrooms or baby potatoes to the slow cooker along with the peppers. They'll absorb the buttery sauce and become tender.

For a thicker gravy, mix 2 tablespoons of cornstarch with 2 tablespoons of cold water and stir it into the sauce during the last 30 minutes of cooking. Let it bubble to thicken.

Variations

Spicy Kick: Add 2 sliced jalapeños or a teaspoon of red pepper flakes along with the peppers for a spicy twist. You can also use a spicy seasoned au jus mix or add a dash of hot sauce before serving.
Mushroom & Onion: Swap the red onion for a yellow onion and add 8 ounces of sliced cremini mushrooms. The mushrooms will soak up the buttery sauce and add an earthy depth.
Beer-Braised: Replace the au jus mix with 1 cup of dark beer and 1 cup of beef broth. The beer adds a malty richness that complements the beef and butter beautifully.
Herb-Crusted: Rub the flank steak with a mixture of dried thyme, rosemary, and garlic powder before adding it to the slow cooker. This adds an extra layer of herbal flavor that pairs well with the cowboy butter.

Storage and make-ahead

Fridge: Refrigerate leftovers in an airtight container for up to 4 days. Reheat gently, adding a splash of broth if needed.
Freezer: Freeze in a freezer-safe container for up to 3 months. Thaw overnight in the refrigerator before reheating.
Reheat: Reheat in a saucepan over medium-low heat, stirring occasionally, until hot and bubbling. Add a little beef broth to loosen the sauce if necessary.

Store leftovers in an airtight container in the refrigerator for up to 4 days. The flavors will continue to meld, making it even tastier the next day. Reheat gently in the microwave or in a saucepan over low heat, adding a splash of beef broth if the sauce has thickened too much.

You can prepare the ingredients up to a day in advance. Slice the steak, peppers, and onion, and store them separately in the refrigerator. When ready to cook, layer everything in the slow cooker as directed. This makes morning assembly even faster.

Serving ideas

Serve the steak and peppers over creamy mashed potatoes to soak up the rich au jus.

The buttery sauce also pairs beautifully with crusty bread for dipping, or over cooked egg noodles for a comforting pasta dish. A simple green salad with a tangy vinaigrette cuts through the richness nicely.

For a low-carb option, serve the steak and peppers over cauliflower rice or alongside roasted vegetables. The dish is also delicious tucked into warm tortillas with a sprinkle of fresh cilantro.

Leftovers make a fantastic sandwich filling—pile the beef and peppers onto a hoagie roll and top with provolone.

Frequently asked questions

Can this recipe be made on high heat instead of low?

Yes, the recipe can be cooked on high for 4 to 5 hours instead of low for 8 hours. The meat will still be tender, but the longer low-and-slow cooking yields the most fork-tender results. Check for doneness by testing if the beef shreds easily with a fork.

What is cowboy butter, and can it be made at home?

Cowboy butter is a compound butter flavored with garlic, herbs, and sometimes spices. It can be made at home by mixing softened butter with minced garlic, chopped parsley, thyme, chives, and a pinch of cayenne. Shape it into a log, chill, and slice as needed.

Can this dish be frozen?

Yes, this dish freezes well. Cool the cooked steak and sauce completely, then transfer to a freezer-safe container. It can be frozen for up to 3 months. Thaw in the refrigerator overnight and reheat gently on the stovetop or in the microwave.

What can be served with this slow-cooker flank steak?

This dish is delicious over mashed potatoes, egg noodles, rice, or crusty bread to soak up the buttery au jus. A side of roasted vegetables or a crisp green salad also balances the richness. For a low-carb option, serve over cauliflower rice.

Why is the meat tough even after cooking?

If the meat is tough, it likely wasn't cooked long enough. Flank steak needs several hours of low heat to break down its connective tissue. Also, be sure to slice the meat against the grain before cooking. If in doubt, continue cooking for another 30 minutes and test again.

Recipe card

Slow-Cooker Cowboy Butter Flank Steak with Peppers

Prep 10 minCook 8 hTotal 8 h 10 minServes 6

Ingredients

2 lb flank steak, thinly sliced against the grain
2 bell peppers (1 green, 1 red), sliced into thick strips
1 red onion, cut into wedges
2 sticks garlic-herb cowboy butter, cut into pieces
1 oz dry au jus mix

Instructions

Place the sliced flank steak strips in the bottom of a 5-6 quart slow cooker, spreading them into an even layer. Scatter the bell pepper strips and red onion wedges over the beef. Place the garlic-herb cowboy butter pieces on top and sprinkle the dry au jus mix evenly over everything.
Cover the slow cooker and cook on low for 8 hours, or on high for 4-5 hours, until the beef is fork-tender and easily pulls apart. The sauce should be bubbling gently around the edges. Do not lift the lid during cooking unless checking for doneness near the end. Let it rest for 3 minutes before slicing.
Turn off the slow cooker and let the beef rest in the sauce for at least 3 minutes before serving. Use a slotted spoon to serve the steak and peppers over mashed potatoes or crusty bread, then spoon some of the buttery au jus over the top.

Contains: milk

Estimated nutrition per serving

Calories: 520
Protein: 35 g
Carbohydrates: 12 g
Fat: 36 g

Automatic estimate from the ingredient list, not laboratory-verified.

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This recipe is based on a short cooking video and is published under the pen name Clara Weller. It was checked before publication, but errors can slip through. Nutrition, when shown, is an estimate. Read more in our editorial policy and on our food safety page.