The Ultimate French Onion Sliced Steak Croissant Sandwich

There are certain flavors that just transport me back to my earliest culinary adventures. For me, French onion soup is one of those anchoring tastes. I remember, as a budding cook, being utterly fascinated by the alchemy of slowly caramelized onions, their sweetness deepening with every stir, eventually yielding a broth so rich and soul-satisfying. This sandwich, in its brilliant simplicity, captures that essence but elevates it into something entirely new and utterly decadent – a true celebration of texture and taste that I can’t wait for you to experience.

Recipe Overview

• Prep Time: 15 minutes
• Cook Time: 35 minutes
• Total Time: 50 minutes
• Servings: 4
• Yield: 4 sandwiches
• Dietary Type: Not specified

Ingredients

This recipe calls for a select few high-quality ingredients that come together harmoniously.

• For the Steak & Marinade:

  • 2 lbs flank steaks
  • 5 tablespoons extra virgin olive oil, divided
  • 2 garlic cloves, minced
  • 2 tablespoons McCormick’s Montreal Brand Steak Seasoning
  • 1 teaspoon hot sauce
  • 2 tablespoons Worcestershire sauce
  • 2 tablespoons red wine vinegar
  • Salt and fresh ground black pepper, to taste

• For the Caramelized Onions:

  • 2 large yellow onions, thinly sliced
  • 1 tablespoon fresh thyme leaves, chopped
  • Salt and fresh ground black pepper, to taste
  • 1 cup chicken broth

• For the Sandwich Assembly:

  • 4 large plain croissants
  • 4 slices Gruyere cheese or 4 slices Emmenthaler cheese

Equipment Needed

• Grill pan or outdoor grill
• Large skillet
• Baking sheet
• Aluminum foil
• Cutting board
• Sharp knife

Instructions

The journey to this incredible sandwich is a straightforward yet rewarding one, involving a bit of patient caramelization and a quick sear.

1. Prepare for Searing: Begin by preheating your grill pan or outdoor grill to high heat. Simultaneously, preheat your broiler.
2. Craft the Marinade: In a medium bowl, combine the minced garlic cloves, McCormick’s Montreal Brand Steak Seasoning, hot sauce, Worcestershire sauce, and red wine vinegar.
3. Emulsify the Marinade: Whisk in 3 tablespoons of the extra virgin olive oil until the marinade is well combined and slightly emulsified.
4. Marinate the Steak: Place the flank steaks in a shallow dish. Pour the prepared marinade evenly over the steaks, ensuring they are thoroughly coated. Gently toss to ensure every surface is covered. Allow the steaks to marinate for a brief but effective 5-10 minutes. This short marination period is key to infusing the steak with those savory, tangy flavors.
5. Caramelize the Onions: While the steak is marinating, heat a large skillet over medium-high heat. Add the remaining 2 tablespoons of extra virgin olive oil.
6. Build the Onion Base: Once the oil is shimmering, add the thinly sliced yellow onions, chopped fresh thyme leaves, and a pinch of salt and fresh ground black pepper. Cook, stirring often, for approximately 7-8 minutes, or until the onions begin to turn a deep, rich golden brown. This gradual cooking process is essential for developing their inherent sweetness.
7. Deglaze with Broth: Pour in the chicken broth. Continue to cook, stirring occasionally, for an additional 2-3 minutes. The goal here is for the chicken broth to reduce and almost completely cook away, leaving the onions wonderfully moist and infused with the savory liquid. Once achieved, remove the skillet from the heat and set the onions aside.
8. Prepare the Steak for Grilling: Remove the marinated flank steaks from the marinade. Pat them dry thoroughly with paper towels. This step is crucial for achieving a good sear on the grill. Discard the remaining marinade.
9. Grill the Steak: Carefully place the dried flank steaks onto the preheated grill. Grill for 6-7 minutes on each side. The exact time will depend on the thickness of your steaks and your desired level of doneness. Aim for a beautiful char on the outside and a tender, juicy interior.
10. Rest the Steak: Transfer the grilled flank steaks to a clean cutting board. Cover them loosely with aluminum foil and let them rest for 5 minutes. This resting period allows the juices to redistribute throughout the meat, ensuring maximum tenderness and moisture in every slice.
11. Slice the Steak: After resting, thinly slice the flank steak on an angle, cutting against the grain. This technique further enhances the tenderness of the steak.
12. Prepare the Croissants: Carefully split the large plain croissants in half horizontally, creating a top and bottom for each sandwich. Place the halved croissants on a baking sheet, cut sides up.
13. Assemble the Base: On the bottom halves of each croissant, generously pile a portion of the caramelized onions.
14. Add the Steak: Arrange a good layer of the thinly sliced flank steak directly on top of the caramelized onions.
15. Top with More Onions: Follow the steak layer with another portion of the caramelized onions. This layering ensures a beautiful distribution of flavors and textures throughout the sandwich.
16. Melt the Cheese: Place a slice of Gruyere cheese or Emmenthaler cheese on top of the onions on each sandwich bottom. Then, place the top halves of the croissants onto the baking sheet as well.
17. Broil to Perfection: Transfer the baking sheet with the assembled croissant sandwiches to the preheated broiler. Broil for 1-2 minutes, or just until the cheese is melted and bubbly, and the cut sides of the croissant tops are lightly toasted. Keep a very close eye on them to prevent burning, as croissants can toast quickly.
18. Serve Immediately: Once the cheese is gloriously melted and the tops are golden, carefully remove the baking sheet from the broiler. Place the toasted croissant tops onto the melted cheese of the sandwich bottoms. Serve these magnificent sandwiches immediately.

Expert Tips & Tricks

• Onion Patience is Key: The magic of French onion soup, and thus these sandwiches, lies in the deep caramelization of the onions. Don’t rush this step. Low and slow heat is your friend here, allowing the natural sugars in the onions to develop without burning. If they start to brown too quickly, reduce the heat further.
• Steak Slicing Precision: Slicing against the grain is non-negotiable for tender steak. Look for the direction the muscle fibers are running and cut perpendicular to them.
• Broiler Watch: Croissants are delicate. Broilers vary in intensity, so stay vigilant during the final broiling stage. You’re looking for golden-brown toasting and melted cheese, not charred edges.
• Ingredient Quality Matters: With so few ingredients, each one plays a starring role. Use good quality steak seasoning and flavorful cheese for the best results.

Serving & Storage Suggestions

These French Onion Sliced Steak Croissant Sandwiches are best enjoyed the moment they come out of the broiler, with the cheese perfectly melted and the croissant warm and slightly crisp. They are a substantial meal on their own, but a light side salad with a simple vinaigrette would be a lovely accompaniment to cut through the richness.

Due to the delicate nature of the croissant and the melted cheese, these sandwiches are not ideal for storing. They are truly a dish best made and enjoyed fresh. If you happen to have any very small leftovers, you could theoretically store them in an airtight container in the refrigerator for up to 1 day. However, reheating them would likely result in a soggy croissant and a less appealing texture. It’s best to plan for this recipe to be consumed immediately.

Nutritional Information

(Note: Nutritional values are estimates and can vary based on specific ingredients and portion sizes.)

Nutrient	Amount per Serving	% Daily Value
Calories	845.2 kcal
Calories from Fat
Total Fat	50.2 g	77%
Saturated Fat	18.1 g	90%
Cholesterol	137.9 mg	45%
Sodium	929 mg	38%
Total Carbohydrate	40.8 g	13%
Dietary Fiber	2.9 g	11%
Sugars	11.8 g	47%
Protein	55.7 g	111%

Variations & Substitutions

• Cheese Choices: While Gruyere and Emmenthaler are classic pairings for their nutty, slightly sweet, and excellent melting qualities, feel free to experiment. Provolone, Swiss, or even a sharp white cheddar could offer delightful variations.
• Broth Base: If chicken broth isn’t readily available, beef broth or even a good quality vegetable broth would work well for caramelizing the onions.
• Herb Power: If you don’t have fresh thyme, dried thyme can be used sparingly (about 1/3 to 1/2 teaspoon) in place of the fresh leaves.
• Vegetarian Twist: For a vegetarian version, omit the flank steak and increase the quantity of caramelized onions. You could also add sautéed mushrooms or roasted bell peppers for more substance.

FAQs (Frequently Asked Questions)

Q: Can I make the caramelized onions ahead of time?
A: Absolutely! Caramelized onions can be made a day or two in advance and stored in an airtight container in the refrigerator. Gently reheat them before assembling the sandwiches.

Q: What kind of flank steak cut is best for this recipe?
A: Look for a flank steak that is relatively uniform in thickness to ensure even cooking on the grill.

Q: My broiler is very intense; how do I avoid burning the croissants?
A: Keep a close eye on the sandwiches and consider lowering your oven rack slightly if your broiler is particularly hot. You can also turn the oven to a moderate bake (around 375°F or 190°C) after the cheese starts to melt to ensure it’s fully gooey without scorching the croissant.

Q: Can I use a different type of bread instead of croissants?
A: While croissants offer a unique richness and flaky texture, you could certainly try other sturdy breads like thick-cut challah or brioche. However, be mindful that they will cook differently under the broiler.

Q: Is there a way to make this dish more filling?
A: You could add a thin layer of thinly sliced roasted potatoes or mushrooms on top of the steak before adding the final layer of onions and cheese.

This French Onion Sliced Steak Croissant Sandwich is more than just a meal; it’s an experience. It takes the comforting, deeply satisfying flavors of classic French onion soup and presents them in an unexpected, delightful format. The flaky, buttery croissant, the richly caramelized onions, and the perfectly seared steak topped with melted cheese create a symphony of textures and tastes that is truly unforgettable. I encourage you to gather these simple ingredients, embrace the process, and savor every incredible bite. Let me know how you make out!