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french onion steak sandwiches on white plate

French Onion Steak Sandwiches

RecipeBoy.com (shared from The Secret Ingredient Cookbook by Kelly Senyei)
The caramelized onions on these sandwiches are boosted with a secret ingredient!
Prep Time 20 mins
Cook Time 1 hr 20 mins
Total Time 1 hr 40 mins
Course Sandwiches
Cuisine American
Servings 4 servings



  • 2 tablespoons unsalted butter
  • 2 medium white onions, thinly sliced
  • One 1-ounce package onion soup mix


  • Two 8-ounce sirloin steaks
  • kosher salt and freshly ground black pepper
  • extra virgin olive oil
  • 4 whole French sandwich rolls, halved
  • 1 cup shredded Gruyere cheese
  • 1 tablespoon freshly squeezed lemon juice
  • 2 cups arugula



  • Heat the butter in a large skillet set over medium heat. Once the butter has melted, add the onions and cook, stirring occasionally, for 20 minutes, until the onions soften and become golden. Reduce the heat to medium-low, then stir in the onion soup mix. Cook the onions, stirring as needed to prevent burning, until they are dark brown and caramelized, about an additional 30 minutes. If at any point the onions begin to burn, add 2 tablespoons of water to the pan and continue cooking. Set the onions aside.


  • Season the steaks with salt and pepper. Coat the bottom of a large skillet set over medium-high heat with olive oil. Once the skillet is hot, add the steaks and cook to your desired doneness. For medium-rare, cook for about 8 minutes, or until they reach an internal temperature of 130 degrees F.
  • Transfer the steaks to a cutting board and let them rest for 10 minutes. Slice the steaks as thinly as possible against the grain.


  • Preheat the oven to broil. Place the four bottom halves of the sandwich rolls on a baking sheet, then divide the caramelized onions among the rolls. Top the onions with the steak and Gruyere cheese. Place the sandwiches about 4-inches under the broiler and broil until the cheese is melted.
  • In a medium bowl, whisk together 2 teaspoons of olive oil and the lemon juice. Add the arugula and a pinch of salt and pepper, then toss to combine. Top the sandwiches with arugula, then add the top halves of the rolls and serve.


Keyword french onion, sandwiches, steak