Thank you to our first round of official Steamy Kitchen Recipe Testers for testing out these incredibly delicious French Onion Steak Sandwiches. Today we are giving away a $50 dinner party gift card and a signed copy of The Secret Ingredient Cookbook written by Kelly Senyei.

This is the perfect recipe to get you into the summer mood. With Summer Solstice right around the corner, this will be your new go-to summer sandwich. They are incredibly flavorful and juicy. Everything you want in a sandwich and more! This incredibly decadent recipe is from Kelly Senyei’s brand new book, The Secret Ingredient Cookbook, and the key and secret ingredient to these perfect sandwiches are a package of onion soup! The foiled lined packet of yummy powdered flavorings that we are all very familiar with and that you will often see in your traditional holiday dishes. 


The onions get caramelized in butter halfway, then the onion soup mix is added to finish up the caramelization process. These perfect caramelized onions are given new life when the onion soup mix becomes mixed in and adds the perfect punch of bite and flavor to your steak sandwiches. While your onions are cooking, you are able to sear off your steaks until they reach a perfect 130F, which should only take about 8 minutes. Once the onions are finished and the the meat is perfectly cooked, the rest of the sandwiches come together in just moments. Finish off your sandwiches with a generous portion of gruyere cheese 

How To Make These French Onion Steak Sandwiches Ahead of Time 

We were curious if this could work, so we tested it out ourselves! We made the caramelized onions the day before and put them in a glass jar in the fridge. Next, we seasoned up our sirloin steaks and seared them off according to the recipe. Instead of slicing them right away, we put them in a glass container in the fridge once they were cooled. 

The next day, 30 minutes before assembling our sandwiches, I pulled the steak and onions from the fridge to come down in temperature. While I preheated the oven, I thinly sliced the sirloin steaks and grated the cheese. Then, I popped my rolls in the oven and tossed my arugula salad ingredients in a bowl. Having the onions and steak prepped ahead of time made the rest of the recipe come together in just moments! We assembled our French Onion Steak Sandwiches, sat down with a cold beer and we were thoroughly satisfied! 

This Recipe is Tested by Our Steamy Kitchen Recipe Testers! Read Reviews Below!

French Onion Steak Sandwiches

Prep Time 20 minutes
Cook Time 1 hour 20 minutes
Total Time 1 hour 40 minutes
Course dinner
Cuisine American
Servings 4 people


  • 2 tablespoons unsalted butter
  • 2 medium white onions thinly sliced
  • 1 1-oz. package onion soup mix
  • 2 8-oz. sirloin steaks
  • Kosher salt and black pepper
  • Extra-virgin olive oil
  • 4 French sandwich rolls halved
  • 1 cup shredded Gruyère cheese
  • 1 tablespoon fresh 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. 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 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°F.
  • Transfer the steaks to a cutting board and let them rest for 10 minutes. Slice the steaks as thin 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 onions among the rolls. Top the onions with the steak and Gruyère cheese. Place the sandwiches under the broiler until the cheese is melted.
  • In a medium bowl, whisk together 2 teaspoons olive oil and the lemon juice. Add the arugula and a pinch of salt and pepper, then toss to combine. Top the sandwiches with the arugula, then add the top halves of the rolls and serve.
Keyword Cookbook Review, Giveaway, Sandwiches, skirt steak recipe
Tried this recipe?Let us know how it was!

Steamy Kitchen Recipe Tester Reviews: 


Marie Egerton: So, we tried this swapping out the olive oil for hemp seed oil, and it was delicious. A small note, I would suggest broiling the base part of the bun plain in the oven for a minute before topping and melting the cheese. (There is plenty of butter in the bun so no need to add that)

Viv Taylor: A truly easy recipe that’s absolutely delicious! I made this for my bf and his two friends and they all loved it. In fact, they all agreed it was restaurant quality good! The dressed arugula was the perfect touch, adding a light citrusy tang that really compliments the richness of the cheese. I tried to follow the recipe as written, but I didn’t have French rolls and just used a loaf of French bread cut into sandwich size. I think it was a little too “bready” as a result. One person suggested adding au jus to help with the “breadiness”, or if you like your sandwich a little more saucy. Second, I added a thin layer of butter on the both the top and bottom halves of bread before broiling. 

And lastly, it wasn’t in the recipe to warm the top halves with the bottom ones, but I did assuming that it would be recommended. Overall, the sandwiches were a hit and I will 100% make again!!

Evelyn Achuck Yue: Tried the French Onion Steak Sandwiches recipe on my family tonight. It was a big hit! I used rib eye steak and French bread instead. I hollowed out the bread a bit so the that it wouldn’t be too “bready” and had a nice ratio of the steak, onion, cheese and arugula. The onion powder mix was the secret ingredient that gave the onions and sandwich a nice umami flavor! Initially, I was concerned that the kids may not like arugula but that wasn’t the case. The lemon and oil gave the arugula a nice refreshing taste without the bitter and peppery taste of some arugula. Will make this recipe for the family again!

Kim Semsel: Made with portobello mushroom caps. Used Gouda cheese. My husband is wolfing it down! The onions make a difference.

Carol Hays: It came out very yummy!! Interesting idea to use the Onion Soup mix! 

To purchase Kelly’s new book, click HERE!


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