Cowboy Butter French Onion Flank Steak Crockpot Dinner

This slow-cooker dinner turns simple ingredients into a rich, savory meal with almost no effort. Thinly sliced flank steak simmers all day with sweet Vidalia onions, beef consommé, and a generous amount of garlic-herb butter.

The result is fork-tender beef in a silky, buttery au jus that begs to be spooned over mashed potatoes. Just layer everything in the Crockpot, walk away, and come back to a dinner that tastes like it took hours of hands-on work.

This recipe is the definition of set-it-and-forget-it cooking. You simply place raw flank steak strips in the slow cooker, top with sliced onions, pour in consommé, and add sticks of garlic-herb butter and a packet of au jus mix.

After several hours on low, the beef becomes meltingly tender and the onions caramelize into sweet, silky ribbons. The butter melts into the sauce, creating a rich, glossy gravy that coats every bite. Serve it over mashed potatoes or crusty bread for a complete, satisfying meal.

Ingredients

Why this recipe works

The slow cooker does all the work here, turning a tough cut like flank steak into fork-tender bites. The low, moist heat breaks down the connective tissue in the meat, while the onions and consommé create a deeply savory cooking liquid.

The garlic-herb butter adds richness and a layer of flavor that infuses the entire dish as it melts.

Using a packet of au jus mix boosts the savory umami without requiring a long list of spices. The consommé provides a concentrated beef flavor that complements the steak.

Because everything cooks together, the flavors meld and develop over hours, resulting in a sauce that tastes far more complex than the sum of its ingredients.

Notes and substitutions

Flank steak is ideal here because it becomes incredibly tender when cooked low and slow. If you can't find flank steak, sirloin or chuck roast also work well. Slice the meat against the grain before cooking to ensure it shreds beautifully later. Vidalia onions are sweet and mild, but any sweet onion variety will do.

Garlic-herb butter is often sold in sticks at the supermarket; look for one with garlic and herbs like parsley, thyme, or chives. If you prefer to make your own, mix softened butter with minced garlic and dried herbs. The au jus mix adds a savory, salty depth—choose a low-sodium version if you're watching salt intake.

• flank steak: sirloin steak or chuck roast, thinly sliced
• Vidalia onions: sweet yellow onions or Walla Walla onions
• beef consommé: beef broth (use 1 1/2 cups for similar richness)
• garlic-herb butter: 4 tbsp unsalted butter mixed with 2 minced garlic cloves and 1 tsp dried herbs

Equipment

• 6-quart slow cooker (Crockpot)
• Cutting board
• Chef's knife
• Measuring spoons
• Serving spoon
• Ladle