Cowboy Butter French Onion Flank Steak Crockpot Dinner Tips, FAQ & printable recipe

Tips for success

For the most tender results, always slice the flank steak against the grain before cooking. This shortens the muscle fibers, so they break down more easily during the long, slow cook.

If you prefer larger chunks, you can cut the steak into 2-inch pieces instead of thin strips—just increase the cooking time slightly.

To make the sauce thicker, remove the beef and onions from the slow cooker, then whisk in a cornstarch slurry (1 tbsp cornstarch mixed with 1 tbsp water) and cook on high for 10-15 minutes until thickened.

You can also add a splash of Worcestershire sauce or a spoonful of Dijon mustard for extra depth.

Variations

• Mushroom Beef: Add 8 oz sliced mushrooms to the slow cooker along with the onions for an earthy, savory twist. Sauté the mushrooms in butter first for extra flavor, or simply toss them in raw—they'll soften as they cook.
• Spicy Kick: Add 1-2 sliced jalapeños or a teaspoon of red pepper flakes to the slow cooker for a subtle heat. You can also use a spicy garlic-herb butter or add a splash of hot sauce to the consommé.
• Cheddar Topping: When serving, sprinkle shredded sharp cheddar or provolone over the hot beef and let it melt. This adds a cheesy, indulgent layer that pairs beautifully with the savory au jus.
• Herb Swap: If you don't have garlic-herb butter, use regular unsalted butter and add 2 minced garlic cloves, 1 tsp dried thyme, and 1 tsp dried rosemary to the slow cooker. This gives a similar aromatic flavor.

Storage and make-ahead

Fridge

Store in an airtight container in the refrigerator 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 warmed through. Add a little beef broth or water to loosen the sauce if needed.

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 on the stovetop, adding a splash of beef broth or water if the sauce has thickened too much.

This recipe is perfect for meal prep. You can assemble the raw ingredients in the slow cooker insert the night before, cover, and refrigerate.

In the morning, place the insert in the slow cooker base and cook as directed. Alternatively, cook the full recipe, cool, and store in portions for up to 3 days in the fridge or 3 months in the freezer.

Serving ideas

Serve the beef and onions over a bed of creamy mashed potatoes, buttered egg noodles, or crusty bread to soak up the sauce.

For a lighter option, spoon it over roasted vegetables or cauliflower mash. Garnish with fresh chopped parsley or thyme if desired, though the dish is delicious on its own.

This dish also works well as a filling for sandwiches or tacos. Pile the beef onto toasted rolls with provolone or Swiss cheese and broil until melted for a French onion–style sandwich. Or serve it over rice with a side of green beans for a complete meal.

Frequently asked questions

Recipe card

Cowboy Butter French Onion Flank Steak Crockpot Dinner

Prep 10 minCook 8 hTotal 8 h 10 minServes 6

Ingredients

• 2 lb flank steak, thinly sliced against the grain
• 2 medium Vidalia onions, thinly sliced
• 1 can (10.5 oz) beef consommé
• 2 sticks (8 tbsp each) garlic-herb butter, softened
• 1 oz dry au jus mix (1 packet)

Instructions

1. Place the sliced flank steak in the bottom of a 6-quart slow cooker. Spread the sliced Vidalia onions over the beef. Pour the beef consommé over the onions and beef. Place the sticks of garlic-herb butter on top, then sprinkle the dry au jus mix evenly over everything.
2. Cover the slow cooker with the lid. Cook on LOW for 8 to 10 hours, or on HIGH for 4 to 5 hours, until the beef is fork-tender and easily shreds or cuts with a spoon. Let it rest for 3 minutes before slicing.
3. Once the beef is tender, remove it from the slow cooker to a cutting board. Use two forks to shred the meat into bite-size pieces, or slice it against the grain into strips. Return the beef to the slow cooker and stir gently to coat with the sauce.
4. Taste the sauce and add salt and pepper if needed. Keep in mind the au jus mix and consommé are already salty, so season cautiously.
5. Spoon a generous portion of the beef and onion mixture over creamy mashed potatoes on a plate. Ladle extra sauce over the top. Serve hot.

Contains: milk, gluten

Estimated nutrition per serving

Calories

520

Protein

38 g

Carbohydrates

12 g

Fat

35 g

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