French Onion Soup Burgers Recipe

Ingredients:
For the Burgers:

1 1/2 pounds (680g) ground beef (80% lean is best for juicy burgers)
1 tablespoon Worcestershire sauce
Salt and freshly ground pepper, to taste
4 burger buns (preferably brioche or soft hamburger buns)
For the Caramelized Onions:

2 large onions, thinly sliced
2 tablespoons unsalted butter
1 tablespoon olive oil
1/4 teaspoon salt
1/4 teaspoon black pepper
1 teaspoon sugar (to help caramelize the onions)
1 tablespoon balsamic vinegar (optional, for extra flavor)
1/4 cup dry white wine (or chicken broth)
For the Soup Sauce:

1/2 cup (120ml) beef broth (or onion broth)
1 tablespoon unsalted butter
1 teaspoon Worcestershire sauce
1 tablespoon Dijon mustard (optional for extra flavor)
1 tablespoon fresh thyme leaves (or 1 teaspoon dried thyme)
1/2 teaspoon garlic powder
For Toppings:

4 slices Swiss cheese (or Gruyère cheese)
Fresh thyme sprigs (for garnish, optional)
Chopped parsley (optional for garnish)
Instructions:
1. Prepare the Caramelized Onions:

Heat 2 tablespoons butter and 1 tablespoon olive oil in a large skillet over medium heat.
Add the sliced onions, salt, pepper, and sugar to the skillet. Stir to coat the onions in the butter and oil.
Cook the onions, stirring occasionally, for about 20-25 minutes, or until they are soft, golden, and caramelized. Be patient, as caramelizing onions takes time. If they start to brown too quickly, lower the heat.
Once the onions are caramelized, stir in the balsamic vinegar (if using) and cook for another 2-3 minutes, letting the vinegar reduce. Then add the white wine (or broth) and cook for an additional 2 minutes, scraping up any brown bits from the pan. Set the onions aside.
2. Make the Burger Patties:

In a bowl, mix together the ground beef, Worcestershire sauce, salt, and pepper. Be careful not to overmix, as this can make the burgers tough.
Form the beef mixture into 4 equal-sized patties, about 1/2 inch thick.
3. Cook the Burgers:

Heat a grill pan or skillet over medium-high heat. Lightly grease the pan with olive oil or butter.
Cook the burger patties for 4-5 minutes per side, or until they reach your desired level of doneness (use a meat thermometer for accuracy: 160°F for medium).
During the last minute of cooking, place a slice of Swiss cheese on top of each burger and cover the pan to melt the cheese.
4. Prepare the Soup Sauce:

In the same skillet where you cooked the burgers, add 1 tablespoon butter and 1/2 cup beef broth. Stir to combine.
Add Worcestershire sauce, Dijon mustard (if using), garlic powder, and fresh thyme. Bring the sauce to a simmer and cook for 2-3 minutes, letting it thicken slightly.
5. Assemble the Burgers:

Toast the burger buns lightly in a toaster or on the grill, until golden brown.
Place the cooked burger patties with melted Swiss cheese on the bottom half of each bun.
Top with a generous portion of the caramelized onions, followed by a spoonful of the savory soup sauce.
Add the top half of the bun, and garnish with fresh thyme sprigs and parsley, if desired.