Thank you to our first round of official Steamy Kitchen recipe testers for trying these French Onion Steak Sandwiches. Today we’re giving away a $50 dinner party gift card and a signed copy of Kelly Senyei’s The Secret Ingredient Cookbook.
Get ready for summer with this rich, flavorful sandwich. With the Summer Solstice approaching, these sandwiches will quickly become a go-to: juicy steak, deeply caramelized onions enhanced with a packet of onion soup mix, and melted Gruyère on a crusty roll. The onion soup mix—familiar from holiday recipes—adds a savory punch that transforms the caramelized onions into something extraordinary. 
The onions are cooked slowly in butter until soft, then finished with the onion soup mix to deepen the caramelization and flavor. While the onions cook, sear the steaks until they reach about 130°F for medium-rare—roughly 8 minutes depending on thickness. Once the meat rests and the onions are ready, assembly is quick. Top with plenty of shredded Gruyère for a melty, savory finish.
How to Make These French Onion Steak Sandwiches Ahead of Time
We tested make-ahead prep and it works beautifully. Make the caramelized onions the day before and store them in a jar in the fridge. Season and sear the steaks as directed, then cool and store the steaks whole in a glass container in the fridge. The next day, remove the steak and onions about 30 minutes before assembling so they come closer to room temperature. Preheat the oven, thinly slice the steak against the grain, grate the cheese, warm the rolls, and toss the arugula with lemon and oil. With the components ready, assembly takes only minutes—serve with a cold beer and enjoy.
French Onion Steak Sandwiches
20 mins
1 hr 20 mins
1 hr 40 mins
Dinner
American
4 people
Ingredients
- 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
Instructions
- Heat the butter in a large skillet over medium heat. Add the onions and cook, stirring occasionally, for about 20 minutes. Reduce heat to medium-low and stir in the onion soup mix. Continue cooking, stirring to prevent burning, until the onions are deep brown and caramelized, about 30 more minutes. If they begin to stick or burn, add 2 tablespoons of water and continue cooking. Set aside.
- Season the steaks with salt and pepper. Heat a large skillet over medium-high and coat the bottom with olive oil. When hot, add the steaks and cook to desired doneness. For medium-rare, cook about 8 minutes or until the internal temperature reaches 130°F.
- Transfer steaks to a cutting board and let rest 10 minutes. Slice as thin as possible against the grain.
- Preheat the oven to broil. Place the bottom halves of the rolls on a baking sheet. Divide the caramelized onions among the rolls, top with sliced steak and shredded Gruyère. Broil until the cheese is melted and bubbly.
- Whisk 2 teaspoons olive oil with lemon juice in a medium bowl. Add arugula, season with a pinch of salt and pepper, and toss. Top sandwiches with the dressed arugula, add the roll tops, and serve.
Cookbook Review, Giveaway, Sandwiches, steak sandwich
Steamy Kitchen Recipe Tester Reviews
Marie Egerton: We swapped olive oil for hemp seed oil and it was delicious. I suggest broiling the base of the bun plain for a minute before topping and melting the cheese since the rolls already have plenty of butter.
Viv Taylor: A truly easy and delicious recipe—restaurant-quality, according to my guests. The dressed arugula adds a bright citrus note that balances the cheese. I used a loaf of French bread cut into sandwich-sized pieces, which felt a bit too bready; one suggestion was to serve au jus if you prefer a saucier sandwich. I also added a thin layer of butter to both top and bottom halves before broiling and warmed the top halves with the bottom. Overall, a hit—I’ll make this again!
Evelyn Achuck Yue: I made this for family night using rib eye and French bread. I hollowed the bread slightly to avoid too much bready texture and kept a good balance of steak, onion, cheese, and arugula. The onion soup mix gave a wonderful umami boost. The lemon-dressed arugula was refreshing without being too peppery—kids liked it. We’ll be making this again.
Kim Semsel: I made the sandwiches with portobello caps and Gouda—my husband loved them. The onions really make a difference.
Carol Hays: It came out very yummy—interesting idea to use the onion soup mix!
To purchase Kelly’s new book, see the listing on retail sites.
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