Slow-Cooker Cowboy Butter Flank Steak with Peppers

This slow-cooker flank steak recipe is the ultimate set-it-and-forget-it dinner. Thin strips of beef simmer all day with colorful bell peppers, red onion, and a generous amount of garlic-herb cowboy butter, plus a packet of au jus mix for deep savory flavor.

The result is spoon-tender meat in a rich, buttery gravy that's perfect over mashed potatoes or crusty bread. Just layer the ingredients, walk away, and come back to a bubbling, aromatic meal that tastes like hours of tending.

Slow cookers are the workhorses of busy weeknights, and this recipe shows why. With just five ingredients and about ten minutes of prep, you can have a hearty, comforting dinner that cooks while you go about your day.

The flank steak becomes incredibly tender as it braises in the buttery au jus, while the peppers and onions soften into sweet, silky strands. This is the kind of meal that makes the whole house smell amazing and delivers on flavor with almost no effort.

Ingredients

Why this recipe works

The slow cooker's low, steady heat works magic on flank steak, a cut that can be tough if cooked quickly. Over hours of gentle braising, the connective tissue breaks down and the meat becomes fork-tender, absorbing the rich flavors of the butter and au jus. The enclosed environment traps steam, creating a moist cooking atmosphere that keeps the beef succulent and prevents it from drying out.

Layer the ingredients in the order given—meat on the bottom, vegetables on top, butter and seasoning last—so the beef is surrounded by moisture and flavor as it cooks. The butter melts and mingles with the au jus to form a luscious gravy that coats every strip. This hands-off method is forgiving and foolproof, making it perfect for busy cooks who want a satisfying dinner without constant attention.

Notes and substitutions

Flank steak is the star here, but sirloin or skirt steak also work well. Slice it thinly against the grain to help it become tender.

The garlic-herb cowboy butter adds a punch of flavor—if you can't find it, soften 4 tablespoons of butter and mix in minced garlic and dried herbs like parsley, thyme, and chives. The dry au jus mix is convenient and gives that deep, savory note; it's available in most supermarkets.

For the peppers, use any combination of colors you like. Green peppers are slightly more bitter, while red and yellow are sweeter. Red onion adds a mild bite that mellows during cooking.

If you prefer a milder onion flavor, use a sweet Vidalia or yellow onion. This recipe is naturally gluten-free if you check that your au jus mix is gluten-free, and it can easily be made dairy-free by using a plant-based butter.

• flank steak: sirloin steak or skirt steak, sliced thin
• garlic-herb cowboy butter: 4 tablespoons unsalted butter mixed with 2 minced garlic cloves and 1 teaspoon dried herbs
• dry au jus mix: 2 cups beef broth plus 1 tablespoon Worcestershire sauce
• bell peppers: any color bell peppers or poblano peppers for a milder heat

Equipment

• Slow cooker (5-6 quart)
• Cutting board
• Chef's knife
• Measuring spoons
• Serving spoon
• Serving plate