1. Caramelize the Onions:
- Prepare the Onions: In a large skillet, heat the butter and olive oil over medium heat until the butter is melted and bubbly.
- Cook the Onions: Add the thinly sliced onions to the skillet, stirring to coat them in the butter and oil. Sprinkle the onions with salt and sugar, which will help with the caramelization process.
- Caramelize: Cook the onions over medium-low heat, stirring occasionally, for about 25-30 minutes, or until they are deeply golden and caramelized. If the onions start to stick to the pan, add a splash of beef broth to deglaze and help them cook evenly.
- Add Flavor: Stir in the fresh thyme leaves and balsamic vinegar (if using) and cook for another 2-3 minutes. Remove the onions from the heat and set them aside.
2. Prepare the Burgers:
- Season the Beef: In a large mixing bowl, combine the ground beef, Worcestershire sauce, garlic powder, salt, and black pepper. Mix gently with your hands until just combined, being careful not to overwork the meat, which can make the burgers tough.
- Form Patties: Divide the beef mixture into four equal portions and shape each into a patty about 3/4-inch thick. Make a small indentation in the center of each patty with your thumb; this helps the burgers cook evenly.
- Cook the Burgers: Heat a grill or grill pan over medium-high heat. Cook the burgers for 4-5 minutes on each side for medium-rare, or until they reach your desired level of doneness. During the last minute of cooking, place a slice of Gruyère cheese on top of each patty, covering the grill or pan to melt the cheese.
3. Toast the Buns:
- Toast the Buns: While the burgers are cooking, melt the butter in a separate skillet over medium heat. Split the brioche buns and place them cut-side down in the skillet. Toast until golden brown and crispy, about 1-2 minutes.
- Add Dijon Mustard (Optional): If you like, spread a thin layer of Dijon mustard on the bottom half of each toasted bun for an extra layer of flavor.
4. Assemble the Burgers:
- Build the Burger: Place a cheesy burger patty on the bottom half of each toasted bun. Top with a generous mound of caramelized onions.
- Top and Serve: Place the top half of the bun on the burger and press down gently. Serve the French Onion Soup Burgers hot, with a side of crispy fries, a green salad, or your favorite burger sides.
Tips for the Best French Onion Soup Burgers:
- Caramelize Slowly: Don’t rush the onions! Slow-cooking them over low heat is key to developing that rich, sweet flavor.
- Quality Cheese: Gruyère is traditional for French onion soup, but Swiss or even a mild provolone can work if you prefer.
- Season Generously: Season both the beef patties and the onions well, as the flavors need to be bold enough to stand out.
Serving Suggestions:
- Wine Pairing: A glass of red wine like a Pinot Noir or Merlot pairs beautifully with these burgers, echoing the deep flavors of the caramelized onions.
- Side Dishes: Consider serving with garlic parmesan fries, a mixed greens salad, or a bowl of French onion soup for an indulgent meal.
Conclusion:
These French Onion Soup Burgers are a true indulgence, combining the rich, comforting flavors of French onion soup with the satisfying bite of a juicy burger. Perfect for a cozy night in or a special weekend treat, this recipe will quickly become a favorite. Enjoy the harmony of sweet caramelized onions, melted Gruyère, and perfectly cooked beef all wrapped up in a soft, toasted bun. It’s the ultimate comfort food fusion!